Storage medium having a layer of micro-optical lenses each lens generating an evanescent field

ABSTRACT

A medium suitable for the optical storage and retrieval of information comprising a substrate, an active layer for retention of the data, and an overlying optical layer, or layers for double-sided. The optical layer serves to produce an evanescent field in or adjacent to the active layer in response to an incident beam of radiation. The evanescent field is frustrated or attenuated by the data in the active layer and produces a signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/728,262, filed Oct. 8, 1996, commonly assigned herewith nowU.S. Pat. No. 5,754,514.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention in general relates to the field of optical recordingsystems and media and, in particular, to storage media comprisingintegral near-field optics by which means a greater resolution andstorage density is attained in the processes of writing to and readingfrom a recording layer.

2. Description of the Prior Art

The following technical articles and authors are relevant to the presentapplication:

Newton

McCutchen

Kino

Gaudiana, R. A., et al, High Refractive Index Polymers, U.S. Pat. No.5,132,430, Jul. 21, 1992, assigned to Polaroid.

Guerra, J. M., "Photon tunneling microscopy," in Proceedings fromSurface Measurement and Characterization Meeting, Hamburg, SPIE Vol.1009, pp. 254-262, 1988.

Guerra, J. M., "Photon tunneling microscope," Paper Summaries, SPSE 42ndAnnual Conference, Boston, pp. 11-15, 1989.

Guerra, J. M., "Photon tunneling microscopy," Applied Optics, Vol. 29,No. 26, pp. 3741-3752, 1990.

Guerra, J. M., "Super-resolution through Diffraction-born EvanescentWaves," Appl. Phys. Lett. 66 (26), p. 3555. 1995.

Guerra, J. M., Plummer, W. T., Optical proximity imaging method andapparatus, U.S. Pat. No. 4,681,451, Jul. 21, 1987. Assigned to PolaroidCorp.

Cronin, D. V., Guerra, J. M., Sullivan, P. F., Mokry, P. A., Clark, P.P., Cocco, V. L., Data storage apparatus using optical servo tracks,U.S. Pat. No. 4,843,494, Jun. 27, 1989. Assigned to Polaroid Corp.

Guerra, J. M., Apparatus and Methods Employing Phase Control andAnalysis of Evanescent Illumination for Imaging and Metrology ofSubwavelength Lateral Surface Topography, U.S. Pat. No. 5,666,197, Sep.9, 1997. Assigned to Polaroid Corp.

Guerra, J. M., Dark Field, Photon Tunneling Imaging System and Methods,Patent Allowed, June, 1997.

Guerra, J. M., Dark Field, Photon Tunneling Imaging Probes, PatentAllowed, June, 1997.

Guerra, J. M., Dark Field, Photon Tunneling Imaging System and Methodsfor Measuring Flying Height of Read/Write Heads, Patent Allowed, June,1997.

Guerra, J. M., Dark Field, Photon Tunneling Imaging System and Methodsfor Optical Recording and Retrieval, Patent Pending.

Guerra, J. M., Apparatus and Methods for Providing Phase ControlledEvanescent Illumination, Patent Allowed.

Guerra, J. M., Phase Controlled Evanescent Field Systems and Methods forOptical Recording and Retrieval, Patent Allowed, Sept. 1997.

N. Bloembergen and C. H. Lee, Phys. Rev. Letters 19, 835 (1967).

Mirabella, F. M. Jr., and N. J. Harrick, Internal ReflectionSpectroscopy: Review and Supplement, Harrick Scientific Corp., Ossining,N.Y. 1985.

A. Yariv, P. Yeh, Optical Waves in Crystals, John Wiley & Sons, N. Y.,1984. Bragg reflection p. 175. Gaussian beams, p. 25. Coupled modetheory, p. 177. Coupled mode theory of Bragg reflectors, p. 194. Formbirefringence, p. 205. Electromagnetic surface waves, p. 209. Guidedwaves and integrated optics, p. 405. Surface plasmons, p. 489. Nonlinearoptics, p. 504. Phase conjugate optics, p. 549.

A. Yariv, Optical Electronics, Holt, Rinehart and Winston, New York(1985). p. 88, Optical resonators, like their low-frequency, radiofrequency, and microwave counterparts, are used primarily to build uplarge field intensities with moderate power inputs. A universal measureof this property is the quality factor Q of the resonator

P. Yeh, Introduction to Photorefractive Nonlinear Optics, John Wiley &Sons, Inc., New York, 1993.

A. Otto, "Excitation of nonradiative surface plasma waves by the methodof frustrated total reflection," Z. Phys. (216), 398 (1968) and (219),227 (1969).

Integrating optics and even micro-optics with a photo sensitive materialis known in other applications not involving data storage, high spatialresolution, or even near-field integration. For example, Polavision™film incorporated temporary lenticular lenses during production for thepurpose of exposing color filter stripes on the emulsion. In the presentstate of the art, micro-optic elements may be added to a CCD imager soas to increase light efficiency by directing incident light away fromthe "dead" gate structures and into the photo-active areas. Many lightdetectors for light measurement or security devices use micro-opticarrays placed near the detector in order to increase the field of viewof the detector.

In near-field optical applications, splitting off the total internalreflection (TIR) surface from the aplanatic immersion lens in an imagingobjective and integrating it with the object to be viewed is taught inGuerra, Applied Optics 1990 and SPIE 1988, and in a flexible form(transducer) in Guerra, J. M., Flexible Transducers for Photon TunnelingMicroscopes and Methods for Making and Using Same, U.S. Pat. No.5,349,443, Sep. 20, 1994 assigned to Polaroid Corp., Guerra, J. M.,Stereoscopic Photon Tunneling Microscope, U.S. Pat. No. 5,442,443, Aug.15, 1995 assigned to Polaroid Corp, and Guerra, J. M., Method for MakingFlexible Transducers for Use with Photon Tunneling Microscopes, U.S.Pat. No. 5,484,558, Jan. 16, 1996. Assigned to Polaroid Corp.Improvements and extensions of that split TIR concept are claimed andwill be shown herein.

While the art describes a variety of optical storage media, thereremains a need for improvements that offer advantages and capabilitiesnot found in presently available instruments, and it is a primary objectof this invention to provide such improvements.

It is another object of the invention to provide for a method of readingand writing utilizing evanescent field resolution.

It is another object of the invention to facilitate use of the nearfield to attain super-resolution in all axes for optical data storagereading, writing, erasing, where the data is stored as index changes(complex, may include absorption), polarization or other phase changes,topographic height changes, etc.

It is another object of the invention to fully utilize the whole-fieldoptical capability for the purposes of: multi-tasking, multi-trackencoding, faster data-transfer rates, faster random access time, morerobust data through redundancy, elimination of radial actuatormechanisms, lower required disc rotation speed, higher track densitythrough reduced cross talk in absence of Gaussian, robustness throughredundancy, multi-channel encoding for higher data density, and multipleprogram simultaneous/interactive play.

It is another object of the invention to eliminate close-flyingrequirement of near-field head by miniaturizing, pluralizing, andintegrating near-field optics to media.

It is another object of the invention to have better control over theflying and have a more stable near field that is integral with themedium by integrating near-field optics to the medium housing.

It is another object of the invention to improve the NA andsignal-to-noise of propagating light optical data storage systems andmedia by integrating optical elements with the medium and/or the mediumhousing.

It is another object of the invention to integrate an internalreflection surface with a recording medium whereby the active layer canbe protected by an overlying surface, such as a diamond-like coating,and whereby full factor of n² is retained.

It is another object of the invention to provide removable, economichigh-density, near-field media.

It is another object of the invention to provide removable, economic,high-density media with integrated optics for an increase in resolutionand storage density by at least a factor of n with or without near-fieldor an immersion medium.

It is another object of the invention to provide a medium in whichinteraction of an integral near-field and the integral active recording,erasable, or ROM layer is either through frustration of TIR orattenuation of TIR.

It is another object of the invention to provide a medium in whichintegral micro-optics are used for optical discerning of data throughinterference, absorption, fluorescence, wavelength, size, height, orreflection differences.

It is another object of the invention to provide a medium in which theintegrated optics are formed by gradient index in a substantially planarsurface.

It is another object of the invention to provide a medium in which theintegrated optics are holographic optical elements (HOEs).

It is another object of the invention to provide a medium in which theintegrated optics can be molded in by injection, injection compression,or compression molding.

It is another object of the invention to provide a medium in which theintegrated optics may be emplaced by means of embossing with heat orsolvent.

It is another object of the invention to provide a medium in which theintegrated optics can be internal, external, or part of an opticalwindow in a protective housing.

It is another object of the invention to produce a near-field in themedium such that its characteristics can be precisely controlled.

It is another object of the invention to allow full use of theattributes of the near-field, including the vertical direction, wherethe stability of it being integral to the medium and not dependent onflying height variations and surface topography.

It is another object of the invention to facilitate use of the saidstable integral evanescent field for multilevel, multi-layer, surfaceplasmon, resonant near-field, diffractive near-field, phase-resolved,wavelength (spectral, fluorescence) and/or other writing and readingtechniques.

It is another object of the invention to provide for an increase inresolution by illuminating the micro-optic integrated medium eitherinside, outside, or at the critical angle, thereby using eitherpropagating light or evanescent near-field.

It is another object of the invention to cause an increase inillumination intensity by: forming a smaller spot, and constructiveinterference in the standing wave that gives rise to the field.

It is another object of the invention to place the active recordingsurface or ROM surface internal to the medium for data protection.

It is another object of the invention to place the micro-optics eitherinternal to the medium or integral to a housing.

It is another object of the invention to provide the prisms in aretro-reflective arrangement such that the photo-active layer resides onall TIR surfaces.

It is another object of the invention to fill micro-prism cavities witha high index polymer of about 1.9-2.1, or to planarize with a sol-gelprocess.

It is another object of the invention to provide a system that can beeither epi-illuminated, dark-field illuminated, or phase-controlledilluminated.

It is another object of the invention to provide a small-format systemfor nomadic personal digital applications.

It is another object of the invention to provide an optical storagesystem that rivals or surpasses the data access speed and density ofnon-removable hard disc drives.

It is another object of the invention to provide integral optics that byvirtue of their small size reduce aberrations normally introduced bysubstitution of a prism for an aplanatic sphere, while enjoying the fullfield of the prism.

It is another object of the invention to provide, in the case of theclose packed array in the window of the cassette, optics with full axisof revolution, thereby regaining factor of n².

It is another object of the invention to provide a plate, eitherflexible or rigid, having integral, internal, or external micro-opticsin the form of a close-packed lens array that can be used forlithography and other energy delivery purposes, microscopic observation,metrology, or other in an oil-less immersion microscope that is low costand regains large working distance, which can be used for interferometryas well as near-field depending on the NA.

It is another object of the invention to provide an integral medium thatincludes diffractive micro-optics which are much smaller than thewavelength and are planes in a crystal, thin film vertical layers,molecular scale polymers, phase gratings induced by holography or ionimplantation or other, with the diffractive optics working alone or intandem with refractive micro optics, said diffractive optics being 1, 2,or 3 dimensional, in order to produce evanescent fields withquasi-wavelengths much smaller than achievable with refractive indexalone.

It is another object of the invention to provide two or more matchedsets of diffractive optics, such that one acts as a reference and theother, when altered by light, creates interference between the two and asignal.

It is another object of the invention to encode the information fromsaid diffractive structures in an analog form.

It is another object of the invention to encode the information fromsaid diffractive structures in a digital form.

It is another object of the invention to provide media with integraloptics that works well with staggered detector array for reduction orelimination of actuator, and subpixel resolution of data, and parallelprocessing.

It is another object of the invention to provide the foregoing featuresto any of a disc, a tape, or a photo-active layer.

It is another object of the invention to integrate light source, optics,diffraction grating, detector, into a flying head.

It is another object of the invention to take integration to itsultimate, an integrated optical chip or macro device in which iscontained some or all of the following components: detector array,illumination array, total internal reflection interface, micro-optics,diffraction subwavelength optics, writeable erasable active layer,resonance layer structure, surface plasmon metal layer, phase resolutionor shifting means, and so on for a true solid state storage device.

It is another object of the invention to use said integrated head inother applications, such as in lithography, in a print head in graphicarts, or as a medical sensor, or as a medical energy delivery device.

Other objects of the invention will be obvious, in part, and, in part,will become apparent when reading the detailed description to follow.

SUMMARY OF THE INVENTION

The present invention results from the observation that evanescentfield, or near-field, illumination and imaging brings a number ofadvantages to optical data storage but the downside is that a flyingnear-field head is normally required, which makes removable media hardto achieve, and may be susceptible to head crashes in portable nomadicdevices. Further, a flying near-field head is sensitive to topographicnoise in the medium, which reduces the signal to noise available fordata. Moreover, for the next-generation near-field embodiments usingdiffraction near-field, phase-controlled near-field, and multilevelnear-field, a controlled and confined near-field is required. Thepresent invention, therefore, integrates the near-field optics, and thusthe near field itself, with the medium, so that parameters important tonear-field performance can be more precisely controlled, and the mediumcan be made removable.

There are two general embodiments of integrating the near field with themedium. In one, the near-field optics are integrated with the cartridge.While the downside is that close-proximity flying is required as withthe discrete flying head, the advantage is that the flying is moreeasily controlled, the flying interface is sealed within the cartridgeso that the medium is easily removable, and the full NA² factor in arealdensity is achieved. Further, radial actuation is reduced or eliminated,with the advantages that that entails.

In the second, the near-field optics are integrated with the mediumproper. The advantage is that flying is completely eliminated, and alsothat the near-field is very well controlled so that increases in datastorage density by means of the various near-field tools usedindividually or in combination (diffraction, phase, multilevel, etc.)can be achieved, again in a removable medium. The downside is that onlya factor of NA ratio (vs. NA²) is achieved in areal density, but this ismore than made up for by the increases otherwise gained. Otherimprovements include whole-field imaging, high SNR, among others, thatare common to either.

Finally, integrating micro-optics with the medium is useful even in thepropagating-light case, where modest increases in areal resolution aregained along with large increases in data transfer rates and reducedrandom access time from the whole-field imaging.

It is difficult for the magnetic data storage industry to achievewhole-field data storage and reading because of the nature of themagnetic read/write transducer. Even hybrids of magnetic and optical(i.e., the magneto-optical technique) suffer from the need for aphysical magnetic coil. While multiple read/write arrays are in use,they cannot be placed so close as to eliminate head movement.

Optical data storage, however, can achieve whole-field capabilitybecause light passes through itself, and multiple photons can be made toexist in any density of a given space. However, the dependence uponinterference as the optical contrast mechanism, and the transfer of themindset of magnetic sequential track recording to optical recording, hasmissed the opportunity to capitalize on perhaps this most importantfeature of optical recording--the ability to image multiple tracks andwhole fields at one time. This innovation, preferably with near-fieldbut also even with propagating light, ends the forced magnetic recordingrestrictions on optical recording and frees it to enjoy its fullpotential.

Other features of the invention will be readily apparent when thefollowing detailed description is read in connection with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and operation of the invention, together with otherobjects and advantages thereof, may best be understood by reading thedetailed description to follow in connection with the drawings in whichunique reference numerals have been used throughout for each part andwherein:

FIG. 1 is a diagrammatic perspective view of a conventional opticalstorage system comprising an objective lens and a medium used for datastorage or retrieval;

FIG. 2 is a diagrammatic elevational view of the conventional opticalstorage system of FIG. 1;

FIGS. 3 through 5 are diagrammatic elevational views of a conventionaloptical reader comprising an objective lens and illustrating diffractioneffects resulting from increasingly smaller data artifacts;

FIG. 6 is a diagrammatic view of the optical reader of FIG. 5 employingan aplanatic lens to increase the resolution;

FIG. 7 is a diagrammatic view of an optical reader, in accordance withthe present invention, comprising an optical layer disposed upon thesurface of a data storage medium;

FIG. 8 is a diagrammatic perspective view of the conventional reader ofFIG. 6;

FIG. 9 is a diagrammatic elevational view of the conventional reader ofFIG. 6;

FIG. 10 is an illustration of the intensity of an evanescent fieldemanating from a reflecting surface;

FIG. 11 is a diagrammatic representation of the evanescent field of FIG.10;

FIG. 12A illustrates the signal-to-noise ratio for information derivedfrom a medium read by means of a conventional propagating illuminationmethod using bright-field microscopy;

FIG. 12B illustrates the signal-to-noise ratio for information in aphase change medium read by means of near-field methods;

FIG. 13 is a diagrammatic perspective view of the optical reader of FIG.7;

FIG. 14 is a diagrammatic view of an optical storage system comprising asource of illumination, an objective lens, and a storage medium inaccordance with the present invention;

FIG. 15 a photomicrograph of a portion of an audio compact discillustrating a plurality of encoded tracks as seen in near-fieldillumination;

FIG. 16 is a diagrammatic view of an alternative embodiment of theoptical storage system of FIG. 14 comprising a dark-field source ofillumination;

FIG. 17 is a diagrammatic cross-sectional view of a storage medium, inaccordance with the present invention, wherein the integral opticallayer comprises dihedral reflector elements;

FIGS. 18 through 20A and 20B illustrate one embodiment of a method usedin fabricating a storage medium comprising integral near-field optics inaccordance with the present invention;

FIG. 21 is a first embodiment of a storage medium in accordance with thepresent invention disposed within a protective housing;

FIG. 22 is a cross-sectional view of the optical storage medium andhousing of FIG. 5, taken through section A--A';

FIGS. 23A and 23B illustrate concentric and spiral configurations ofdata storage on a circular disc;

FIGS. 24A and 24B illustrate rectilinear and rotational configurationsof data storage on a rectangular medium;

FIG. 25 is a diagrammatic cross-sectional view of the storage medium ofFIG. 4 showing a layer of optical material disposed upon an active,data-storage layer;

FIG. 26A is a second embodiment of a storage medium in accordance withthe present invention comprising a protective housing and an opticalwindow;

FIG. 26B is an alternative embodiment of the storage medium of FIG. 26A;

FIG. 27 is a cross-sectional view of the storage medium of FIG. 7, takenthrough section B--B';

FIG. 28A is diagrammatic cross-sectional view of the storage medium ofFIG. 26B showing a layer of optical material spaced apart from anactive, data-storage layer;

FIG. 28B is an alternative embodiment of the storage medium of FIG. 28Acomprising convex facets;

FIG. 28C is an alternative embodiment of the storage medium of FIG. 28Acomprising concave facets;

FIG. 29A is an alternative embodiment of the storage medium of FIG. 26Acomprising lenticular lenses disposed at an acute angle to the mediumdata tracks;

FIG. 29B is an alternative embodiment of the storage medium of FIG. 26Bcomprising a micro-optical array disposed at an acute angle to themedium data tracks;

FIG. 30 is a third embodiment of a storage medium in accordance with thepresent invention comprising a layer of optical material disposed uponan active, data-storage layer, a protective housing, and a slideablecover retained over an opening in the housing;

FIG. 31 is a cross-sectional view of the storage medium of FIG. 30,taken through section C--C' and in use with external writing/readingoptics;

FIG. 32 is diagrammatic cross-sectional view of the storage medium ofFIG. 31 showing a layer of optical material spaced disposed upon anactive, data-storage layer and optically coupled to an external flyingsplit aplanat;

FIG. 33 is a diagrammatic cross-sectional view of a resonant structureused in conjunction with a conventional aplanatic lens;

FIG. 34 illustrates a storage medium comprising a series of pits ofconstant length and pitch against which a recorded pit pitch variesalong the track causing a heterodyne signal to vary;

FIG. 35 illustrates a storage medium comprising a simple parallel linepattern of constant pitch with recorded lines varying in pitchperpendicular to track direction;

FIG. 36 is a diagrammatical cross-sectional view of an optical storagesystem reader/writer illustrating placement of an annular aperture, or alaser diode array, or a mask, when used for various methods ofwhole-field writing;

FIG. 37 is a diagrammatical plan view of a detector array placed alongand oriented parallel to the longitudinal axis of an optical element, inthe focal plane of the optical element, and disposed over data tracks;

FIG. 38 is a diagrammatical cross-sectional view of a whole-fieldimaging system in accordance with the present invention;

FIG. 39 is a diagrammatical view of a form of vertical storage, utilizedwith integral evanescent fields and referred to as multi-layer, whereinthe total reflection interface at which the evanescent fields arise havebeen replicated vertically with the addition of layers of high-low-highrefractive index materials to the storage medium; and,

FIG. 40 are oscilloscopic traces obtained from signals returned from astorage medium having a four-layer configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Background of the Invention

There is shown in FIGS. 1 and 2 a standard optical storage system 10comprising an objective lens 11, such as found in a Digital VersatileDisc (DVD) head, and a conventional recording medium 20, such as anoptical or magneto-optical recording disc. Recording medium 20 typicallycomprises a recording layer 23 disposed upon a substrate 21, with datarecorded by means of optical artifacts 27 formed in medium surface 25 asit moves relative to objective lens 11, as indicated by arrow 19.

Recording medium 20 may further comprise a transparent protective layer29 disposed on medium surface 25. The reading of data is accomplished bymeans of incident illumination 13 of wavelength λ, a portion of which isreturned to a detector (not shown) as reflected radiation 15 dependingon the presence or absence of optical artifacts 27. When using "epi"(i.e., "from above"), or "oblique," illumination, the resolution of asystem such as optical storage system 10 is typically no greater than##EQU1## where NA is the numerical aperture of objective lens 11, and λis the wavelength of the illumination. The working distance for opticalstorage system 10 is typically on the order of 10 mm.

The numerical aperture is given by the product of the index ofrefraction of the medium (in which recording layer 23 is immersed) withthe sine of half of the angle that the illumination subtends in thatmedium. The numerical aperture is invariant (e.g., the value remainsconstant) when the optical path crosses a planar boundary between twomedium of differing refractive indices. The numerical aperture can beincreased by means of: i) increasing the subtended angle throughrefraction at an interface with an optical element such as a prism oraplanat, or ii) increasing the index of refraction in the immersionmedium which may be the prism or aplanat, or iii) both of the former.This results in a larger numerical aperture and a correspondingly higherresolution.

Information in the form of optical data is typically written to mediumsurface 25 with incident illumination 13 provided essentiallyperpendicular to medium surface 25. As shown in FIG. 3, incidentillumination 13 is diffracted from medium surface 25 when the size ofoptical artifacts 27 (i.e., data) is approximately the same asillumination wavelength λ. The diffraction angle depends on both theillumination wavelength λ (i.e., a longer wavelength results in a largerdiffraction angle) and the spatial period of the data (i.e., a smallerspatial period results in a larger diffraction angle). The spatialperiod of the data is the center-to-center separation "P" of opticalartifacts 27 as shown.

For the data to be resolved and measured, such that a first opticalartifact 27 is distinguishable from a neighboring artifact 28, it isrequired that: i) objective lens 11 be sufficiently large in diameter(or in numerical aperture) to intercept at least a first orderdiffraction 15b, at the minimum diffraction angle θ, and ii) there besufficient intensity difference between first optical artifact 27 andneighboring artifact 28 for first optical artifact 27 to be visible(i.e., modulation is present). First order diffraction 15b combines witha zeroth order diffraction 15a to form an image. (This descriptionfollows the diffraction theory of image formation for a microscope inaccordance with Abbe and Zernike). Interception of even higher orders,if present, serves to contribute to image quality. The numericalaperture can also be thought of as the bandpass which allows onlycertain spatial frequencies to pass. (It should be understood that, inthe examples provided, illumination perpendicular to the recordingsurface is shown for purposes of clarity and that practice of theinvention is not limited to such perpendicular illumination. Obliqueillumination, when used, allows the second order diffraction (not shown)into the numerical aperture for about a factor of two betterresolution.)

As the density of stored information is increased, it becomes necessaryto utilize a smaller optical artifact 27' in the process of writing toor reading from recording medium 20, as illustrated in FIG. 4. Theseparation between optical artifacts 27' is correspondingly decreased aswell. However, because diffraction angle θ' has increased, objectivelens 11 here does not intercept first order diffraction 15d. Onesolution is to use a larger objective lens 11' (indicated by dottedlines). As is well-known in the relevant art, storage density increasesas the factor NA² (i.e., the square of the numerical aperture). In theconventional DVD optical storage system, for example, the objective lensused has an NA of 0.65 rather than the conventional NA of 0.4 so as toprovide for an increase in storage density. However, this approachresults in an increase in cost and more critical tolerances resultingfrom a shallower depth of field.

Alternatively, decreasing the wavelength of incident illumination 13will decrease diffraction angle θ such that first order diffraction 15dintercepts objective lens 11, and optical artifacts 27' are resolved. Ascan be appreciated by one skilled in the relevant art, the search for anillumination source of ever shorter wavelength will continue in view ofthe fact that storage density can be increased in proportion to thesquare of the ratio of conventional (e.g., red) wavelength to a shorter(e.g., blue) wavelength.

As the density of stored information is further increased, an evensmaller optical artifact 27" is utlilized in the process of writing toor reading from recording medium 20, as illustrated in FIG. 5. A firstorder diffraction 15e results and is parallel to medium surface 25. Thisdiffracted illumination is in the form of an evanescent field 39, ornear-field. This non-propagating, non-radiating illumination does notleave medium surface 25. As is understood by one skilled in the relevantart, the amplitude of the illumination decreases exponentially withdistance from medium surface 25. For still smaller optical artifacts,the exponential decay is more rapid.

FIG. 6 illustrates the use of an aplanatic sphere 31 in combination withobjective lens 11 for the detection of artifacts 27" by means ofevanescent field 39. Numerical aperture and resolution are defined anddetermined by the extreme ray in the illumination cone. For a "pure"spatial frequency object as substantially embodied by the diffractiongrating formed by the optical data tracks, the first and primarydiffracted order angle can be made to coincide with the extreme ray ofthe numerical aperture, which allows the optical approximation of theaplanatic sphere with prismatic elements, such as an array of prismmicro-optics.

FIG. 7 illustrates the use of an array of prismatic elements 115 inconjunction with objective lens 11 to provide for detection of artifacts27" by means of evanescent field 39. The resulting field of view isimproved over the aplanat configuration as each prismatic element 115allows every part of the active optical layer occluded by its base to beviewed. In comparison, the aplanat configuration allows only the central50 to 75% of the underlying active optical area to be viewed. Theaplanat has the better resolution, however, because it is optimized toeliminate spherical aberration. Therefore, the aplanat is preferred, ineither its lenticular form or its close-packed two-dimensional form foruse in a configuration integral to a housing (discussed in greaterdetail below). In such configurations, the fields of view of adjacentaplanatic optical elements can be made to overlap, forming anessentially complete field of view with little or no loss of recordingcapability or real estate.

The two-dimensional aplanat increases the areal storage density by thesquare of the ratio of the increase in numerical aperture NA. Thelenticular aplanat, on the other hand, increases the areal storagedensity in the track pitch dimension by only the ratio of the increasein numerical aperture compared to the objective without the integralmicro-optic. As can be appreciated by one skilled in the relevant art,an aplanat configuration is not the preferred choice for integrationwith the medium proper because of the loss of field of view, and a prismform would be used. From an optical standpoint, this is acceptablebecause, given the micro scale of the optics, the aberrations introducedby the planar facets of the prism are minimal compared to the curvedsurface of the aplanat. Only the first order diffraction from thespatially pure optical data structure is required, and it easily passesfrom prismatic element 115 to objective lens 11.

It has been proposed that resolution can be increased with aconfiguration such as that exemplified by a near-field optical storagesystem 30, shown in FIGS. 8 and 9, comprising an objective lens 11' andan aplanatic sphere 31 having a substantially planar surface 32positioned at a distance "d" from medium surface 25 of a conventionalrecording medium 20'. Because the illumination wavelength λ is reducedby a factor equal to the index of refraction of aplanatic sphere 31, theresolution of optical storage system 30 is increased over that ofoptical storage system 10 such that proportionately smaller opticalartifacts 47 can be read. Incident illumination 33 is directed intoaplanatic sphere 31 at an angle greater than critical angle Θ_(C) (heremeasured relative to an optical axis normal denoted by O_(A)). Anevanescent field 39, generated at surface 32, provides for the operationof optical storage system 30.

Incident illumination 33 is totally internally reflected at surface 32to emerge as either totally-reflected radiation 37 or frustrated toproduce propagating radiation 35 by the process of, for example,absorption, refraction, diffraction, or scattering, by optical artifacts47 present in recording layer 23. In practical applications, "d" is lessthan a wavelength λ. Accordingly, there is typically provided little orno protective layer in recording medium 20' so as to enable placement ofaplanatic sphere 31 at the requisite distance. Where a protective layeris used, this is commonly done solely to prevent oxidation of, forexample, magneto-optical (MO) surfaces. Because the illuminationwavelength λ is reduced by a factor equal to the index of refraction ofaplanatic sphere 31, the resolution of optical storage system 30 isincreased over that of optical storage system 10 such thatproportionately smaller optical artifacts 47 can be read.

Optical storage system 30 incurs several disadvantages when operating asa dynamic system in which there is relative movement between aplanaticsphere 31 and recording medium 20. Most problematic is that theoperations of reading and writing are adversely affected by the presenceof contamination on medium surface 25 because the flying height ofaplanatic sphere 31 is made to exceed the sensible extent of evanescentfield 39. This may require that optical storage system 30 be a costly,sealed system. Additionally, because there is no protective layer,active layer 23 is exposed to ambient atmosphere and is vulnerable tooxidation or head crashes.

Propagating and Evanescent-Field Illumination:

With propagating illumination, the highest NA possible at a medium(e.g., greater than one and typically as high as 1.25) is achieved inthe case where the micro-optic array is directly on the medium. For asplit flying integrated micro-optic (described below) and withpropagating illumination, an NA of approximately 0.95 can be realizedwith a flying height much larger than for the near-field case. In eithercase, propagating illumination requires a contrast mechanism such asinterference or polarization analysis, for example, to detect theoptical data. The evanescent field micro-optic enjoys an NA of greaterthan one and typically about 1.25 or more, and also brings all theattributes of near-field illumination to bear, as discussed in greaterdetail below.

As shown in the diagram of FIG. 10, an evanescent field, having anintensity described by graph 80, arises at the boundary between surface32 and the adjacent lower index medium (usually air or another low-indexmedium). Evanescent field 80 is a continuation of the internal standingwave in aplanatic sphere 31 that in turn is a result of constructiveinterference of incident and reflected illumination at surface 32 (i.e.,the TIR interface) that gives rise to evanescent field 80. Therefore,immediately at the active layer or low-index side of surface 32, theresultant intensity 38 can be four times as much as the intensity ofincident radiation (see FIG. 11). Because of this higher intensity, lesssensitive active layers, lower power sources, or lower cost sources canbe used in the associated optical storage system. For writing, the powerlevels provided by coherent laser diodes may still be desirable forpresently-available active optical materials.

"Near-field" is traditionally understood to include both propagating andnon-propagating radiation near (i.e., within a wavelength of) a surface.The non-propagating field is also known as an evanescent field,comprised of inhomogenous or surface bound waves. The evanescent fieldarises in the condition of total internal reflection (TIR) at a boundarybetween a high and low refractive index media, where the parent field inthe higher index medium penetrates into the lower index medium (i.e.,the refraction angle becomes imaginary). Because the time average ofthis penetration of energy (represented by the Poynting vector) is zero,total reflection is indicated. In the quantum mechanical view, thispenetration of the TIR barrier is called photon tunneling. Evanescentfields also arise in other situations, such as when propagatingillumination is diffracted by a grating with grating period smaller thanthe wavelength, discussed below, such that the diffracted orders areevanescent (i.e., the diffraction angle becomes imaginary).

For p-polarized coherent illumination at the critical angle θ_(C) andfor total reflection:

    θ.sub.C =sin .sup.-1 n.sub.21                        (1

where n₂₁ ≡n₂ /n₁ ≡N, the ratio of the indices of refraction in medium 2and medium 1, respectively, the reflected beam is shifted in phase by π,as with reflection by a perfect conductor. (In fact, the totalreflection surface can be treated as a lossless metal.) Littman showedthat, for an absorbing rarer medium, there is no longer a particularangle for total reflection, but a transition of finite angular width.Accordingly, it should be understood that for the present application,when the active layer is an absorber, reference to the critical angletakes into account this finite angular width. Many physical opticstextbooks (e.g., Born and Wolf) proceed from Maxwell's equations to showthat standing waves are established normal to this totally reflectingsurface, internal to the denser medium, because of the superposition ofthe incoming and reflected waves. This results in a net field at thesurface in the rarer medium, normal everywhere to the surface in the Zaxis, with intensity E due to coherent addition (net) of the incidentand reflected beams, evanescent wavelength λ _(e) and phase angle α:

    E=2 cos (2πz/λ.sub.e +α)                   (2

Evanescent field 80 has an amplitude that decays exponentially withdistance from surface 32. The strength of available evanescent field 80is given by: ##EQU2## where E_(o) is the phase dependent amplitude ofthe electric field associated with the photon in the medium comprisingaplanatic sphere 31 and, d_(p), is the penetration depth in the lessdense medium at which E_(o) decreases to E_(o) /e and where: ##EQU3##

and λ₁ is the wavelength in the denser medium, θ is the incidence angle,and n₂₁ in the ratio of denser to lower indices of refraction at theboundary surface 32. The actual penetration depth, where E_(evanescent)falls to the limit of detectability, is dependent on these variables aswell as both the photodetector sensitivity and the sample opticalproperties, and is typically approximately 0.75. However, the evanescentfield, however small in intensity, can exist sensibly for tens ofwavelengths, if the parameters in equation (2) are optimized. Theevanescent field has electromagnetic field vectors in all spatialdirections, so that coupling is made to dipoles in any spatialorientation. This fact is used to advantage in spectroscopy and alsohere, in optical data storage, for more efficient coupling into theactive layer.

The evanescent field can exist in the active optical layer. In therelevant art, this is denoted as attenuated total reflection (ATR).Alternatively, the evanescent field can exist adjacent to the activeoptical layer, denoted as frustrated total reflection (FTR or FTIR). Ineither case, the evanescent field is partly or totally converted intopropagating illumination by the active optical layer, which then formsan image. Both ATR and FTR, as well as propagating, are claimed in thepresent invention in combination with micro-optics integral to themedium.

If evanescent field 39 can be accessed and converted back intopropagating illumination so that it contributes to image formation, itfollows that optical artifacts of a size much smaller than illuminationwavelength λ can be resolved. To access this evanescent field requiresclose proximity to the medium surface because evanescent field 39 decaysover a distance of only a fraction of a micron--hence the term"near-field." Moreover, the smaller the size of the optical artifacts,the smaller the required distance to the medium surface.

To convert evanescent field 39 back into propagating, it is requiredthat one is close to the surface with: i) a high-refractive indexdielectric material, or ii) a diffraction grating with grating periodsimilar in size to the otical artifact spatial period. The moreevanescent the field (i.e., the smaller the optical artifacts), thehigher the refractive index that is required. Ultimately, there is apractical limit (imposed by the index of refraction of availablematerials) of about 2.4 in the visible spectrum to about 3.5 in the nearinfra-red spectrum. Conversion by diffraction is limited only by thediffraction grating spatial period. In the present state of the art, forexample, a diffraction grating spatial period of less than 40 nanometershas been achieved.

Also of importance to optical storage density is the contribution of theexponential vertical decay of the near-field. This exponential decaymakes the contrast of the written optical artifacts extremely high, asthe signal changes from total reflection of the illumination to almosttotal transmission with, in the case of actual optical artifacts, adepth change of only 0.2 microns. In the case of the phase changematerial, the contrast is also increased. The near-field illuminationreduces surface or Fresnel reflection, and is strongly controlled by theabsorption part of the complex refractive index of the phase changematerial. This causes the signal-to-noise, or contrast, of the opticalartifacts to be greatly enhanced over viewing in normal illumination.FIG. 12B illustrates the increase in signal-to-noise ratio forinformation in a phase change medium read by means of near-field methodsas compared to a conventional propagating illumination method usingbright-field microscopy shown in FIG. 12A.

Description of the Preferred Embodiments

There is shown in FIGS. 13 and 14 a generalized diagrammatical view ofan optical storage system 100 comprising an objective lens 111, an epiillumination section 110, and a storage medium 120 in accordance withthe present invention. Objective lens 111 may be the objective of anoptical disc drive or other similar device, such as the objective of amicroscope. Storage medium 120, which may be flexible or rigid,comprises an optical layer 113 overlying an active layer 123 and maycomprise a substrate 121, such as polycarbonate disc or card, or amylar-based tape, to provide physical support to active layer 123.Optical layer 113 comprises a reflection surface 117, disposed on oradjacent to a data surface 125 of active layer 123, and a distributedstructure of micro-optical elements 115, preferably configured asprismatic elements. Alternatively, active layer 113 and substrate 121may comprise a single layer. It should be understood that storage medium120 may include an enclosing housing or cartridge (described below) toprovide protection for the enclosed medium proper and to facilitateloading into and removal from a storage drive device.

Active layer 123 may comprise a "write once" material, a read onlymaterial, or a material in which the written data can be "erased" (i.e.,a rewriteable material). For example, active layer 113 may comprise anyof the optically-active materials used in conventional optical storagemedia, such as magneto-optical (MO), phase change materials, and laserablation surfaces (resulting in surface "pits" or "bumps"). As can beappreciated by one skilled in the relevant art, additionaloptically-active materials that would benefit from integration withmicro-optical elements, in accordance with the present invention,include: photoresist, photorefractive polymers or crystals,photopolymers, chalcogenide glasses and compounds, photographic silverhalide or other emulsions, fluorescently active materials, andsemiconductor structures such as CCD or CMOS silicon detectors. Examplesof photo-refractive materials include LiNbO₃ and BaTiO₃. Example of aphase change material is an alloy such as Te_(x) Sb_(y) Ge_(z) or Te_(x)Sb_(y) Ge₂ Se_(w) (which is erasable).

The optical layer is, in one embodiment, the distributed structure ofmicro-optical elements 155, which may comprise an array of lenticularlenses (i.e., lenses having facets curved in one meridian), prism-likeoptics, or holographic optical elements, for example, or an array ofmicro-lenses (i.e., lenses having facets curved in at least twomeridians), or one or more planar optical layers used in conjunctionwith said elements or, for example, an external aplanat, as described ingreater detail below.

A data bit, represented by the presence or absence of one or moreoptical artifacts 127, is written to or read from data surface 125 bymeans of radiant energy transmitted into optical layer 113. This radiantenergy produces an evanescent field 139 which is used to either readfrom data surface 125 or, when increased to an appropriate intensity orduration, to write to data surface 125. Reading and writing areperformed as storage medium 120 is moved with respect to objective lens111 and illumination section 110. Optical artifacts 127 comprise a localportion with change in polarization (Kerr rotation), optical phase,index of refraction, absorption, scatter, diffraction angle, criticalangle, reflection, material phase state (e.g., crystalline toamorphous), or topography, in comparison to surrounding material.

Illumination section 110 comprises a radiation source 101 and istypically transmitted by means of a beam splitter 102. Epi illuminationbeam 133 is incident upon one or more micro-optical element 115 at anangle of incidence Θ_(E) with respect to the optical axis of opticallayer 113. For angles of incidence Θ_(E) greater than the critical angleΘ_(C) of optical layer 113, there will be produced evanescent field 139adjacent reflection surface 117 and local to micro-optical element 115,at least a portion of which field will lie within active layer 123.Evanescent field 139 provides the means by which optical artifacts 127are detected (i.e., read) or produced (i.e., written). That is, thepresence of optical artifact 127 will produce a detectable attenuationor frustration of evanescent field 139 as evanescent field 139 passesover optical artifact 127, and may result in the conversion ofevanescent field 139 into propagating radiation 135 as described ingreater detail below. Accordingly, the detection of optical artifacts127 is preferably accomplished by means of one or more detectors 104,which may comprise, for example, a detector array or one or morecharge-coupled devices (CCDs), which sense propagating radiation 135passing through beam splitter 102.

Radiation source 101 is preferably of narrow bandwidth and may, forexample, comprise a light-emitting diode such as a blue LED, a laser, alaser diode, or a broadband source of radiation optically coupled to oneor more narrow bandpass filters or a monochromator, so as to limit thetransmitted wavelengths to predetermined ranges. A coherent lightsource, such as a laser, produces an output with side lobes which is notdesirable for use in reading because of cross-talk with adjacent tracks.The preferred source for reading is an incoherent source because itallows the full theoretical resolution of the optics and provides forwhole-field imaging. Typically, an illumination source for the processof reading will comprise an LED because of the relatively low powerlevel required. For the process of writing, a laser source is generallyused because of a higher level of power required. Because the presentsystem has whole-field capability, it becomes possible to use aplurality of laser sources to write multiple tracks concurrently. Wherethere is an erasable (i.e., rewritable) storage medium used, the processof erasing is accomplished by modulating both the intensity and durationof the illumination incident upon the active layer.

Incoherent illumination may be provided by low-cost LEDs, such ascurrently available high-resolution blue LEDs. The incoherence reducesthe ringing of coherent sources that is the cause of cross-talk betweendata tracks. Cross-talk prevents propagating coherent systems from usingthe full theoretical resolution derived from considering the NA andwavelength alone, so that, for example, the new DVD format, withcoherent laser diode illumination, has a track pitch of 0.74 micronswhile at the wavelength and NA of the format, a track pitch of 0.4microns would be possible with incoherent light. Is can be appreciatedby one skilled in the relevant art that, while incoherent light resultsin the highest spatial resolution, incoherent light can be used innear-field optics and cannot be used in interference-based opticalsystems. Similarly, coherent light makes imaging multiple tracks andlarge fields difficult to achieve, while the incoherent light used innear-field allows whole-field multi-track imaging. FIG. 15 is aphotomicrograph of a portion of an audio compact disc illustrating aplurality of encoded tracks as seen in near-field illumination.

Illumination section 110 may further comprise a phase controller 103 forcontrolling the phase of direct illumination beam 133 as it impingesupon optical layer 113. As described in greater detail below, phasecontroller 103 and its functions may be provided by a number ofdifferent means and preferably operates in response to externalelectronic circuitry (not shown). Accordingly, when phase controller 103is used in optical storage system 100, detector 104 comprises a phaseanalyzer.

Oblique Illumination and Imaging:

In a preferred embodiment, best seen in FIG. 16, illumination section110 is not used. Rather, read/write illumination is provided by means ofan illumination section 112. Illumination section 112 comprises aradiation source 101', a focusing lens 119 for providing an illuminationbeam 134 oblique to optical layer 113 and, optionally, a phasecontroller 103'. There is also shown an oblique objective 119', anoptional phase controller 123', and detector 121' when used withillumination section 112.

In this embodiment, the illumination is again reflected light fromabove, as in the epi illumination, but the illumination and imaging axesare not coaxial and are equally oblique to the optical normal axis, and,unlike the tilting objective in the propagating case where the integraloptical layer is a lenticular aplanatic cross section, the obliquityhere is fixed. The entire base of the prism is seen at once, and thetilt and defocus introduced are very small according to the small sizeof the integral optical element. If the oblique objective is actuatedradially, then all defocus is removed as it traverses the integraloptical element. While the actual NA of the objective is considerablyless than one, the oblique incidence and viewing angle provide for aneffective numerical aperture of considerably greater than one, becausethe NA is defined and measured at the sample plane, in this case thebase of the integral optical element. If the oblique head (where thehead comprises both the imaging/detection objective lens as well as theopposed illumination source) is incident at less than the criticalangle, the illumination is propagating and can be used in the normalfashion, such as interference, for example. If the incidence is atgreater than the critical angle, the illumination is evanescent with allthe attributes discussed brought to bear. At each of the extremes of theprism base, one or the other of the first order diffraction is occultedby the prism itself or by a neighboring prism, but the remaining firstorder is sufficient to form an image with the zero order. For thisarrangement, the cone subtended by the objective need not match theangle subtended by the prisms. For example, the integral prism elementsmay be 45°-90°-45° prisms, with the objective being NA 0.65.

Dihedral Reflector Elements

In yet another embodiment, shown in FIG. 17, the integral optical layercomprises dihedral reflector elements 116, wherein incident and exitinglight from the reflector elements undergoes at least two internalreflections from the surfaces forming the dihedral angle, one or both ofwhich reflections may be a total internal reflection. The active layeris coated onto the external faces of the dihedral reflector elements,with optional intervening layers disposed for resonance or otherpurposes as discussed earlier. The external head is incident normal(perpendicular) to the plane of the medium. Data 114 is stored on,preferably, only one of the internally reflecting surfaces. The opticalartifact either restores total internal reflection in an otherwisefrustrated TIR field, or frustrated total internal reflection in anotherwise totally reflecting field, or is simply a propagating lighteffect. The advantage in this embodiment is that it eliminates the needfor planarizing the internal integral micro-optics with a high-indexmaterial as before, while providing the same internalizing andprotection of both the optics and the data associated with the activelayer. While one of the surface pairs is sacrificed for reflection ofthe data, the data surface area is increased by a factor of the squareroot of 2, for only a small total reduction of data surface area. Withpolarization differentiation, data may be stored on both of the internalreflection surfaces.

Fabrication of Optical Layer

The masters for the micro-optic arrays can be fabricated by any one of anumber of well-known techniques, including precision computer-controlleddiamond turning, photolithography, multiple-beam laser lithography,laser mastering lathe, or e-beam lithography. As shown in FIGS. 18, 19,and 20A, a master 201 is fabricated from which an inverse master 203 isformed. Master 201 can be replicated either directly or in a materialsuch as electro-less nickel, for example, to form inverse master 203.Inverse master 203 would be used in a fabrication process such ascompression, injection, or sequential injection/compression molding ofany of a number of plastics such as polycarbonate, acrylic, and others.Alternatively, inverse master 203 can be used for embossing micro-opticsinto a polymer web.

In fabricating master 201, a servo structure (not shown) can be formedto produce a corresponding servo pattern 211 in inverse master 203 to bereplicated onto a micro-optical structure 213. In this manner, there isassured accurate registration between servo pattern 211, which is usedfor tracking in the reading and writing operations, and micro-opticalstructure 213. Alternatively, servo pattern 211 can be embossed,stamped, or otherwise formed into micro-optical structure 213 in asecondary operation in which registration is achieved by known opticalalignment methods, including Moire interferometry. Following theformation of micro-optical structure 213, there can be added an activelayer such as a phase change layer 217 and a protective layer 219, forexample, as well as an optional resonant structure layers or a low-indexFTIR layer. In an alternative embodiment, shown in FIG. 20B, amicro-optical structure 213' comprises truncated prism-like elements.

Fabrication of Micro-Optics

Internal micro-optics that have been formed by embossing, stamping,molding, or otherwise must be filled with an optical material having anindex of refraction sufficiently larger than the host substrate materialto maintain the critical angle for TIR. So, for a host substrate ofpolycarbonate with an index of refraction of 1.5, the concavemicro-optics may be filled with a high index polymer of about 1.9 to 2.1(see Gaudiana '430). This may be done in a two-shot molding operation,or the high index polymer may be spin-coated onto the substrate. Otheralternatives include depositing ZrO₂, ZnS, or other high-index materialinto the micro-cavities by magnetron sputtering or other vacuumdeposition technique, followed by a planarizing operation as is known inthe microelectronics industry. Here, the small amount of materialdeposited requires the micro-cavities to be very small, on the order ofa micron in pitch. Many high-index materials may be applied with asol-gel technique, although the host substrate will have to be of aplastic that can withstand the required solvents and high temperatures.For specialized non-rotational applications, the internal micro-opticsstructure may be formed from a preform drawn down to the requireddimensions.

The optimum size of the micro-optic is determined by mastering,manufacturing, and optical design considerations. Mastering techniquesnow available suggest a pitch size of not too much below 3 to 5 microns,while embossing techniques become problematic with sizes greater thanabout 50 microns. Optical aberrations in the prismatic approximation ofthe aplanatic sphere are minimized as the optic becomes smaller, whilethe number of data tracks per optic is optimized for the larger opticsizes.

Storage Medium with Integral Optical Layer

In a first embodiment, as best seen in FIGS. 21 and 22, data is writtento or read from a storage medium 140 comprising an optical layer 153integral with an active layer 143 preferably disposed upon a substrate141. In the configuration shown, storage medium 140 is disc-shaped, andoptical layer 153 comprises a plurality of concentric or spirallenticular lenses (see for example, FIG. 23) wherein storage medium 140is rotated for the reading and writing of data. In an alternativeembodiment (see FIG. 24), storage medium 140 may be rectangular in shapewith data retrieval and storage accomplished by means of rotation orrectilinear motion, for example. Alternatively, storage medium 140 canbe stationary with data retrieval accomplished by means of a whole-fieldimaging detector array. Storage medium 140 may be disposed within anoptional protective housing 105, as shown. Housing 105, which serves tominimize the possible contamination of active layer 143, comprises anoptically-transparent window 106 to provide for access for the writingof data to and the reading of data from active layer 143.

As best seen in FIG. 25, active layer 143 comprises a material having anoptical property that change state to produce an optical artifact 147within a data surface 145 upon exposure to a sufficient intensity andduration of direct illumination beam 133. In the preferred mode, directillumination beam 133 is incident on a reflection surface 157 at anangle of incidence greater than critical angle Θ_(C) of a truncatedprismatic micro-optical element 155 such that there is generated anevanescent field 159, at reflection surface 157 proximate illuminatedmicro-optical element 155, extending into active layer 143. It should beunderstood that there may be more than one optical artifact 147 in datasurface 145 lying beneath one micro-optical element 155, and thatreading or writing of data would be performed as objective lens 111 andillumination beam 133 are translated relative to optical layer 153.

The index of refraction n₁ of optical layer 153 is preferably greaterthan either the index of refraction n₂ of active layer 143 or the indexof refraction n₃ of optical artifact 147. The change in state of opticalproperty resulting in the production of optical artifact 147 can be achange in index of refraction (e.g., from n₂ to n₃). Alternatively,there may be a change of state in polarization, in phase, in scatter, orin topography. These changes in optical property may be produced by theapplication of direct illumination beam 133 contemporaneously with theapplication of an external magnetic field (not shown). The process ofreading, or detection, makes use of the fact that, in the absence ofoptical artifact 147, direct illumination beam 133 is emitted frommicro-optical element 155 as reflected radiation 137, and where opticalartifact 147 is present, there is produced an attenuation of totalinternal reflection and propagating radiation 135 is emitted toobjective lens 111. In an alternative embodiment, objective lens 111 maycomprise a bifocal feature 231.

In an alternative mode, the illumination source comprises a directillumination beam 133' incident at an angle less than critical angleΘ_(C). In this alternative mode, evanescent field 159 is not produced,but the resulting resolution is still greater than that of aconventional optical storage system.

Storage Medium with Optical Window

In a second embodiment, as best seen in FIGS. 26 and 27, data is writtento or read from a storage medium 160 comprising a housing 171, anoptical-layer window 173, and an active layer 163 preferably disposedupon a substrate 161. As best seen in FIG. 28A, a data bit isrepresented by the presence or absence of one or more optical artifacts167 detected within a data surface 165. Active layer 163 and substrate161 are disposed within housing 171. Optical-layer window 173 comprisesa distributed structure of micro-optical elements 175, such as an arrayof lenticular lenses (as shown) or alternatively, an array ofmicro-lenses. During the process of detecting or producing opticalartifacts 167, active layer 163 is translated relative to objective lens111, as indicated by arrow 19, and data is written to or read fromactive layer 163 through optical-layer window 173.

During the read/write processes, reflection surface 177 of optical-layerwindow 173 is retained at a substantially fixed distance Δz from datasurface 165, preferably on the order of one wavelength of directillumination beam 133. In the preferred mode, direct illumination beam133 is totally internally reflected from reflection surface 177 at anangle of incidence greater than critical angle Θ_(C) of micro-opticalelement 175 such that there is produced evanescent field 179 atreflection surface 177 extending away from illuminated micro-opticalelement 175 and into active layer 163. In the configuration shown,evanescent field 179 is frustrated by the presence of optical artifact167 encountered within active layer 163. The complex index of refraction(n+ik) of active layer 163 is greater than the index of refraction(n_(o)) of the material (typically air) present between reflectionsurface 177 and data surface 165.

In one alternative embodiment, shown in FIG. 28B, storage medium 160comprises optical-layer window 173' comprising a distal surface withconcave curvature (with respect to the medium) for optical correction.In another alternative embodiment, shown in FIG. 28C, storage medium 160comprises optical-layer window 173" comprising a distal surface withconvex curvature for facilitating proximal flying.

Propagating Case

While a medium with integral near-field optics is preferably used torealize the many attributes and applications, many, but not all of whichhave been described here, of the evanescent field component of thenear-field, there are also benefits to be gained by using the integralnear-field optics for only the propagating illumination component of thenear-field. This is accomplished by i) illuminating the integralmicro-optics with an incident angle no greater than the critical anglewithin the micro-optics, such that there is no total internal reflectionwithin the micro-optics and hence no evanescent field, or ii) bychanging the index of refraction of one or more of the following:micro-optic optical layer, active optical layer, intervening opticallayers if present, such that there is no critical angle, or the criticalangle is so large as to be outside of the illumination cone. In eitherof the former, all light is propagating and no evanescent fields exist.

If the integral micro-optics are integral to the medium proper,numerical apertures of greater than 1 can still be achieved as in theevanescent field case, but the other attributes of the evanescent fieldare absent. The optical operation in this case is simply that of animmersion microscope as invented by Abbe in the 1880's. Resolution, andtherefore data storage density, is increased over that of the originalobjective in air by a factor of the ratio of the numerical apertures,for the lenticular micro-optics, and by that ratio squared when themicro-optics comprise full figures of rotation.

If the micro-optics are integral to the medium cartridge such that thereis a layer of air between the optics and the medium proper, thenumerical aperture can be no greater than 1 in this propagating lightcase. All light at greater numerical apertures would be totallyinternally reflected. Here the layer of air can be much greater inthickness than in the case of the evanescent field. Flying heights ofmany wavelengths become allowable, because the light is propagating.Each of the micro-optic elements in combination with the externalobjective or objective array comprise a conventional high numericalaperture "dry" objective, as they are known in microscopy. For bestoptical performance, the surface of the micro-optic elements facing theactive optical layer may be concave, and all surfaces may have asphericcurvatures which are easily molded into, for example, plastic optics. Asin the evanescent field case, the micro-optic elements are preferablyfull figures of rotation and are staggered in an array such that theirfields of view overlap so that there are no areas of the active opticalsurface that are not imaged.

In both of these cases the advantage is an increase in optical datadensity, with a larger flying height in the latter and some reduction ofnoise from topographic roughness of the active optical layer, ifpresent, in the former. However, the optical contrast and signal tonoise enhancement contributed by the evanescent field illumination isabsent. Contrast can be regained by reverting to, in the case ofread-only-media, an interference detection method, requiring topographicpits coated with an aluminum layer, as is well known and practiced now.Other active optical layers, such as magneto-optical, phase change, orother, would exhibit the same degree of optical contrast as they do nowin propagating light, which is to say less contrast than with evanescentfield illumination but sufficient contrast to work. The micro-optics, byvirtue of increasing the numerical aperture and reducing the writingspot size, also function as light intensifiers, which can be utilized infaster writing speeds or lower power laser diodes.

Propagating configuration of optics integrated with housing

In a configuration wherein the medium is illuminated by propagatingillumination, each of the optical elements comprising the micro-opticarray in the housing can have the required optical power and surfacedisposed on both sides of the optic. This configuration will allow themaximization of numerical aperture, resolution, and field-of-view whilekeeping optical aberrations to a minimum by methods generally wellunderstood and known to one skilled in the relevant art.

Integrating a micro-optic array to the cartridge housing the new DVDmedium, for example, would increase the numerical aperture from theexisting 0.6 to about 0.95 for a substantial increase in areal density,and is backward compatible with the DVD system.

Integral Optical Layer as Interference Reference

The optical layer integral to the medium has been generally discussedherein is used, among other things, to increase the areal storagedensity whether the evanescent or propagating illumination is used.There is also an increase in optical contrast and signal to noiseenjoyed in the former, while in the latter the optical contrast is muchlower but sufficient. For ROM or other media where the optical artifactsare read by optical interference techniques, and propagatingillumination is used, the integral optical layer may function as acontact or proximal interference reference plate, such that theinterference is of the first order that is the black center in thecolored Newton interference fringes, for example. While the verticalrange is not as large as for the evanescent field case, the contrast issimilar. This is sometimes known as contact interference microscopy, buthas not been applied to optical data storage heretofore because of theabsence of a proximal interference reference at the medium. In this way,even with propagating light the signal to noise ratio can be enhanced,while eliminating the need for a metallic reflecting layer in the mediumand phase analysis optics in the drive.

In fact, while the first order interference provides the highestcontrast with broadband and white light, additional vertical range andvertical data encoding can be obtained with this interference when thecolored interference fringes are included. With the use of appropriatenarrowband color filtration anywhere in the optical path, or alternatelythe use of plural light sources of different illumination wavelengths,data of only a specific wavelength may be passed to the exclusion of theothers. Thus, information from multiple vertical layers, or evenoverlapping optical artifacts in the same layer, may be separated. Thesurface of the optical layer facing the drive may, as before, beprismatic, lenticular, or planar, and may be used in combination with anoptical lens array, a single lens, or a flying optical head.

Near-field form of optics integrated with cartridge

For the near-field illumination, the side of the micro-optic arrayintegral to the cartridge and facing the medium can be planar, butpreferably will have slight convex curvature in order to optimize thelow-flying characteristics required by the exponential decay of thenear-field.

Flying heights for the micro-optic array integral to the cartridge.

Near-field requires flying heights of typically 0.1 microns for highcoupling strength. That the intensity is increased by the constructiveinterference in the parent wave allows some tolerance here, in that evena higher flying height will still result in adequate signal.

For the propagating illumination, flying height can be several orders ofmagnitude greater than for the near-field.

The micro-optic array integral to the cartridge can be on the surface ofthe window and protected by a moveable shutter, or can be internal tothe window and filled and substantially planarized with a high-indexoptical material (see Gaudiana polymer patent).

Optical Window Configuration

FIG. 29A illustrates a window configuration wherein lenticular lenses221 are oriented at an acute angle to data tracks 223, and FIG. 29Billustrates a window comprising an array of micro-optical lenses 225oriented at an acute angle relative to adjacent data tracks 223.

Storage Medium with "Split" Optics

In this embodiment, as best seen in FIGS. 30 and 31, there is shown astorage medium 180 comprising a housing 191, an aplanat layer 185, andan active layer 183, which is preferably disposed upon a substrate 181.An opening 193 is provided in housing 191 to allow access to activelayer 183. Storage medium 180 may further comprise a sliding cover 195(shown in FIG. 30 only, for clarity) as a means of minimizing the entryof contaminants into housing 191. Data is written to or read fromstorage medium 180 by means of a flying split aplanat 109 disposedbetween active layer 183 and objective lens 111 in a configuration bestexplained with reference to FIG. 32.

Reading and writing of data is accomplished by positioning flying splitaplanat 109 within opening 193 such that an aplanat surface 108 ispositioned substantially within 0.1 μm of optical surface 186. Directillumination beam 133 is totally reflected at aplanat surface 108 and anevanescent field 107 is generated. Evanescent field 107 is opticallycoupled into split-optical layer 185 to produce a secondary evanescentfield 107'. Split aplanat 109 combines with split-optical layer 185 toform an equivalent aplanat, as indicated by dotted lines at 109'. A databit is represented by the presence or absence of one or more opticalartifacts 187 detected within a data surface 184. During the processesof detecting or of producing optical artifacts 187, active layer 183 istranslated relative to flying split aplanat 109, as indicated by arrow19.

The advantage of this configuration is that the greater spacing betweenhead and medium allows for relative movement. The evanescent field isburied in the medium. It then becomes possible to use a high-indexmaterial, such as diamond, for the top part of the split head to takeadvantage of this greater index value and achieve a higher NA, withdiamond-like carbon (DLC) coating on the medium.

In the above manner, the TIR surface portion of the flying head isintegrated with the medium. The flying head may be part of a drive, ormay be a lens array in the housing. The flying height is less than awavelength such that the coupling between the flying head and the layerin the medium is via the evanescent field, and FTIR. In this way, thereis no need for spherical aberration correction, because none isintroduced by such a small split. Further, numerical apertures ofgreater than 1 can occur in the medium. Further still, these numericalapertures can be used for either propagating light immersion imaging, orevanescent field illumination with the attributes already discussed.Others knowledgeable in the relevant art had proposed a split where aportion of the flying aplanatic sphere head is removed, and the opticalequivalent added to the medium. However, the flying heights are on theorder of many wavelengths, such that (1) all the light ispropagating--no use of evanescent fields is made, (2) numericalapertures are restricted to less than one, and (3) the large split andthe absence of evanescent coupling introduces spherical aberration whichmust be corrected for. The see Guerra 1994 patent and 1988 paper showedhow the TIR portion can be split from the head, or objective, with thecoupling between the two, in one embodiment, being immersion oil, butneed not be. Accordingly, in another paper (MRS, 1994), Guerra showedthat the coupling between the TIR surface and the next TIR surface canbe via the evanescent field (Mica image). So, there are at least twoevanescent field couplings here, the first being between the partitionedhead and a first layer in the medium (FTIR), and the second andsubsequent being between the optical layer(s) and the active layer(s)via FTIR or ATR.

In a near-field optical data storage system where the near-field head isflying, this invention allows the optical data surface (ROM or WORM orrewriteable) to be internal to the medium disc (floppy or rigid) ratherthan on the surface of the disc. The optical data is protected, and isalso very planar, thereby removing the noise contributed by topographicvariation of surface data in the near-field and increasing thesignal-to-noise of the system. All the advantages of the integralmicro-optic media configuration are enjoyed, along with the higherstorage density that comes from the numerical aperture being high alongthe track direction as well as perpendicular to the track direction, andwith a disc that is simpler in construction and therefore less costly tomake. This split near-field flying head invention is compatible and canbe combined with dark-field, dark-field near-field, phase near-fieldresolution, diffraction near-field, optical track discrimination,sub-pixel synthesis detector, vacuum surface head, multi-level,multi-layer, and other aspects of our near-field storage technology, aswell as with the Isis phase change material or topographic pits.

A flying near-field head, which is an optically transparent body in theform of a prism or, preferably, an aplanatic sphere that is flying atsubstantially sub-micron height proximal to a disc or other geometrysurface, is disclosed in our 1987 patent as well as later patents fromothers (Stanford, IBM, Matsushita). Typically, the head is illuminatedbeyond the critical angle to generate an evanescent or near field whichis then used to write on and read an optical data surface immersed inthe field.

In the present invention, the near-field head is physically split intotwo parts along a plane parallel to the total reflection surface. Thelarger part may be considered the refractive element, and the remainingthin plate part contains the total reflection surface. The two parts areplaced very close together, without touching, so that they are opticallycoupled by the evanescent field between them. The thin plate part isthen extended and made integral to the medium disc, so that there can berelative movement between the remaining head and disc, and thus flying.At flying heights of less than 0.1 micron, the coupling loss is minorand tolerable. The thin plate may be polycarbonate cut from a web, ormay be a diamond-like carbon or other material layer for higher index ofrefraction and better durability. The thin plate and flying head are oflike indices of refraction.

The near-field and the optical data surface(s) are internal to the disc,with the robustness and precision control inherent to thatconfiguration. However, here only the bottom planar portion of the opticis integral to the disc, while the refractive part is flying. In thissense it is similar to the patented flexible transducer, in which thebottom total reflection surface is a separate flexible sheet placed onthe sample, except that in that case the coupling of the sheet to therefractive optic in the objective is with oil immersion, while in thiscase the coupling is via the evanescent field from the flying head. Thusan evanescent field is generated twice, once at the head/mediuminterface, and then at the medium top sheet/recording layer interface.

Now, the head is flying above a very smooth polycarbonate or othermaterial planar surface so that flying height is much more uniform.Also, the optical data layer is no longer on the surface, vulnerable tohead contact, finger contact, or other hazards. Further, in the case ofphase change data layers, the phase change material is deposited againstthe internal smooth polycarbonate or other surface (there may be otherlayers of other refractive indices deposited first) so that there is notopographic noise source. Full resolution inherent to a discrete flyingnear-field head is enjoyed along with the robustness of the integralmicro-optic media, but without the difficulty of making such media. Nostorage area is lost to field-of-view.

Resonant structure:

It is well known in the relevant art that evanescent field 80 can beenhanced by orders of magnitude with a resonant structure 34. Typically,resonant structure 34 comprises two layers added to the total internalreflection surface of the near-field optic, such as a prism or aplanaticsphere 31, for example. For a prismatic element comprising a materialhaving an index of refraction of 1.5, one added layer will comprise alower index of refraction (e.g., 1.0) and the other layer will comprisea higher index layer waveguide of over 2.0. An absorber adjacent to thehigh index waveguide will exhibit enhanced absorption. This techniqueand structure is well known and is used in spectroscopy, for example.Harrick shows such a structure, seen in FIG. 33, comprising an absorberlayer 36a, a cavity film 36b comprising a high-index material such assilicon, a film reflector 36c comprising a material such as quartz, anda hemicylinder 36d. Yariv and Yeh discuss such resonant structures indepth. Guerra 1994 patent claims a resonant layer structure incombination with a flexible transducer for use in photon tunnelingmicroscope devices, which utilize the evanescent or near field. Guerraadditionally claims a resonant structure with a flying near-field headand also integral to a medium, both for optical data storage in 1997patents, but in combination with phase controlled evanescent fields.Kino shows a thin film on top of the active recording layer (1992optical data storage patent) but the film is not claimed for resonance,and is of an index matching that of a flying head.

Here, the resonant structure may be either part of the near-fieldoptical array integral to the cartridge, or may be integral to themedium proper. In either case, an advantage gained is the largeenhancement of the near-field for much higher signal to noise ratio SNRand absorption. Thus, even very small optical effects (polarization,refractive index, or other changes) in the active optical data recordinglayer are amplified.

In an application wherein the micro-optics are configured as part of ahousing structure for an enclosed optical medium, another advantage isthat the optical array may be molded in plastic, with the performanceand cost benefits inherent to that technique (e.g., mass productionmethods to provide complicated aspheric surfaces by which to reduceaberrations). However, because the waveguide layer in the resonantstructure (which is added to the plastic optical array with the usualvapor deposition techniques) is of a significantly higher index, thespatial resolution and thus areal density of a higher index near-fieldoptic are enjoyed.

In the case of the resonant structure added to the medium proper, theactive optical layer is protected by the added structure fromenvironmental damage. In addition, the application of these layerstypically has a smoothing effect on the topography of the active opticallayer, in the case of MO or phase-change materials, for example, thusreducing the noise from that factor. The relative refractive indices ofthe layers, and their optical thickness, as well as the incidentillumination angle and wavelength, are optimized in well known relationsfor resonance conditions, with many possible variations which areoutside the scope of this invention. Coherence is required for thisresonance.

Alternatively, a surface plasmon resonant field (which also decaysexponentially) may be formed when a layer of about 200 angstroms ofaluminum, gold or silver, disposed between the optical layer and theactive layer, is optically pumped by the evanescent field, and canachieve at least ten times the sensitivity of the evanescent field alonebecause resonance is easily "detuned" by small changes in the adjacentoptically active layer. Ref: Otto.

Further Embodiments

As was disclosed above, to convert evanescent field 39 back intopropagating, it is required that one is close to the surface with i) ahigh refractive index dielectric material, or ii) a diffraction gratingwith grating period similar in size to the artifact spatial period. Themore evanescent the field (i.e., the smaller the optical artifacts), thehigher the refractive index that is required. Ultimately, there is apractical limit (imposed by the index of refraction of availablematerials) of about 2.4 in the visible spectrum to about 3.5 in the nearinfra-red spectrum.

Conversion by diffraction, on the other hand, is limited only by thediffraction grating spatial period. In this case, the diffractiongrating period is less than the illumination wavelength λ, where thegrating can be a phase grating, an amplitude grating, or an indexgrating.

The use of evanescent fields generated by diffractive structures foroptical heterodyning beyond the limitations set by the light wavelengthand refractive index has been disclosed before in Refs. 1-3 andparticularly regarding optical data storage capacity in Refs. 4 and 5.Ref Guerra 1995 APL paper, and '97 phase patent. Any heterodyningtechnique responds best to global (i.e., multi-element), or semi-global,changes rather than local changes (i.e., a single element) in either thereference or unknown frequencies, where an element is a single line pairin the case of a grating, for example.

Encoding diffraction near-field information:

This is a preferred method of making use of the super-resolved opticalstorage capacity of diffraction-born evanescent field opticalheterodyning disclosed previously.

A reference frequency in the form of a substantially sub-wavelengthoptical grating placed within the evanescent field distance to anoptical storage medium replaces the electronic reference frequency nowused in analog optical video storage, thereby allowing optical data tobe stored at similar substantially sub-wavelength dimensions.

Recording and playback of video images (and soundtrack) requiresenormous data storage capability that is best accomplished with afrequency modulation (FM) analog readout and heterodyning technique. Onthe successful laser video discs, for example, the information is storedoptically as pits of constant length in the track direction, but whosepitch varies about some nominal pitch. The analog signal thus generatedis heterodyned with an electronic signal of the constant nominal pitch,or frequency. (Audio, with the less stringent storage demand, is encodeddigitally as pits of varying length.)

In the present invention, the reference electronic signal of constantfrequency is replaced with a reference evanescent field. This isaccomplished with a grating whose period is smaller than theillumination wavelength. The reference grating can take at least twoforms. The first would be a series of pits of constant length and pitch,illustrated in FIGS. 34A and B, against which the recorded pit pitchwould vary along the track, causing the heterodyne signal to vary. Thisis the closest evanescent, or near-field, analog to what is practicednow, except that it is all optical and extends the storage density amagnitude or more. The second reference pattern is a simple parallelline pattern of constant pitch, illustrated in FIGS. 35A and B, with therecorded lines varying in pitch perpendicular to the track direction.The typical track pitch of laser discs is about 1.6 microns (DVD isless). As shown in Ref. 4, a track pitch of 0.1 microns has been easilydemonstrated in the evanescent field. A track pitch of 0.05 microns iscertainly attainable, so that even allowing for a redundancy of about 3tracks, required for a good signal-to-noise in the heterodyning, yields0.15 microns, or a factor of ten over the current technique. Soundtrackscan be recorded by modulating the grayscale of the tracks, or otherdimension, as is done now.

This reference sub-wavelength grating may be in the form of topographyadded to the total reflection distal surface of a discrete flyingoptical head, or may be integral to the optical recording medium itself.The sub-wavelength diffractive grating may be part of the optical layerin the medium (as in FIG. 10, for example) and may be illuminated witheither propagating or evanescent illumination. There may also be asecond reference sub-wavelength diffractive grating disposed between theactive layer and the optical layer. Writing with a diffraction-bornenear-field requires the phase control of the evanescent field as taughtin U.S. Pat. No. 5,666,197 issued to Guerra.

As can be appreciated by one skilled in the relevant art, any of theabove-described embodiments may comprise one or more additional featuresas may be desired to enhance implementation of the disclosed invention.For example, the cartridge may have internal non-woven fabric wipers tokeep the flying interface clean, and may have the usual sliding shutterto protect the integral micro-optic window, as is known in the art.Similarly, abrasion resistant optical hard-coats such as diamond-likecarbon (DLC) can be applied to all exposed and tribological surfaces,such as the medium proper, both side of the integral micro-optic arrayin the cartridge, and the top surface of the micro-optic integral to themedium proper. Further, a head or back plate opposite the medium fromthe flying integral near-field optics may be provided to facilitateproximity flying.

Critical angle method:

In this method, optical artifacts are formed and read when totalinternal reflection is locally frustrated or locally enabled by changein the refractive index of the base or active layer, and illuminationand/or imaging is restricted to just at the critical angle. This methodis sensitive to changes in index of refraction occurring out to thethird decimal place. Changing incident and imaging angle slightlyswitches channels to whole new set of data at a different index andcorresponding critical angle. The illumination can be restricted to theimmediate neighborhood of the critical angle by placing an annularaperture 227 in the illuminator, as shown in FIG. 36. When used inwholefield writing, a laser diode array 229 may be emplaced as shown.Alternatively, laser diode array 229 may be replaced by a mask (notshown) when used for lithography or other such methods of whole-fieldwriting.

Principal Angle Method

The s- and p-polarization components have generally different phaseα.sub.⊥ and α.sub.|| respectively: ##EQU4## where i≡√-1, λ_(o) is thefreespace wavelength of the illumination, β=(N² sin² θ-1)^(1/2), λ₁ isthe wavelength in medium 1, and μ≡n₂ /n₁ ≡n₂₁ ≡N, the ratio of theindices of refraction in medium 2 and medium 1, respectively.

Equations (5) and (6) indicate that phase shifting of the incidentillumination can be accomplished in a number of ways that includewavelength shift, incident angle shift, azimuthal incident angle shift,polarization shift, or shifting of the incident phase in the Z axis. Theillumination may be coherent, or simply filtered white light. The methodused in some interferometer microscopes, for example, can be used, wherepiezo-controlled nanometer physical manipulation of the wavefront phaseis effected, which has the advantage of decoupling phase shift fromamplitude variation. All this is prior art, described in (ref 1997Guerra phase patents).

The difference in (5) and (6) results in the elliptical polarizationseen in totally-reflected illumination. There exists a Principal angleat greater than the critical angle and less than π/2 where the twopolarizations are equal; in this sense it is complementary to theBrewster angle for propagating illumination.

Adjusting the aperture in the illumination such that only illuminationat or near the principal angle reaches the active optical layer willresult in the highest sensitivity to induced or existing polarizationdifferences, representing optical data, in the optically active layer.

Systems:

Objective lens 111 is preferably articulated to enable motion in severaldegrees of freedom such as transverse motion, longitudinal focusing, andtilt. Although prisms are the preferred embodiment, aplanats can be usedand articulating the objective lens would increase the field of view forthe case when optics are aplanatic and integral to the medium proper.

The integrated micro-optics in either form (part of medium proper orpart of medium cartridge) could be read with a substantiallyconventional radially actuated traversing head/objective, and stillenjoy a degree of whole-field and multi-track imaging and the resultantattributes described earlier.

The objective can be a conventional DVD objective, but a more optimizedsystem would include an aspheric objective that corrects for theanamorphic optics of the integrated micro-optics in the medium proper,and corrects for the spherical aberration and astigmatism introduced bythe substitution of prisms for aplanats. Also, the optimized objectivemay be bifocal, with the central part of the numerical aperturecorresponding to the NA less than 1 at the active optical layer focusedon the lands between the truncated prisms. These lands may contain servotracking structure spaced about 0.9 microns apart.

The micro-optics integrated with the medium proper can be typicallyanywhere from 5 microns to 50 microns or more in pitch, with the datatracks on the order of 0.1 micron or so, so each element of themicro-optic looks at many tracks.

However, the integration of micro-optics and the medium allows theopportunity for an improved way of reading and writing optical datawhich reduces or eliminates the need for radial actuation, andultimately, even the need for spinning circular media and data tracks.

Radial actuation reduces the speed of random access of data.Additionally, in systems that utilize a flying head, whether near-field,optical, magneto-optical, or magnetic, most head crashes and resultingdata loss occur during radial movement of the head.

For whole-field imaging, a secondary array of objective optics may beused in conjunction with the integrated array. Similarly, the detectoris not a single element but instead may be an array of elements, with asingle or multiple elements dedicated to each of the optical arrayelements. Just as with the integrated micro-optic array, the optics inthe secondary array can be optimized by aspherizing and can have opticalpower on either side in order to optimize the combined microscopic arraysystem.

If the diameter of the field of view of each of the optical elements inthe array is 50% of the physical diameter of each optic, then it followsthat at least two rows of elements are required, staggered such thatfull coverage is achieved. Additional rows may be included for morehighly optically optimized coverage, or the elements may have discretefocal properties to eliminate the need for focus actuation.

If the detector array is skewed with respect to the optical array, or ifthe elements themselves are offset by a known amount, sub-pixelresolution results and then the secondary optical array can even beeliminated.

For writing, the power levels provided by coherent laser diodes arestill required at this time for the existing active optical materials.However, writing multiple tracks can be achieved through the samesecondary objective optical array if a laser diode array is used inconjunction with it.

Array Objective

So far, it has been assumed that there is a conventional objective inthe drive into which the medium with integral optics is inserted.Further, the objective associated with the drive may not beconventional, but may be fully articulated to include tilt, and may havea bifocal design to better image the servo tracks. Further still, theobjective associated with the drive may be an array of close-packed andstaggered lenses arranged so as to cover the entire area of the mediumwhen the medium is spinning, or when the medium is stationary andsmaller.

However, the objective in the drive may be eliminated by transferringits optical functionality to the optics integral to the medium. This maybe done for either the evanescent field illumination embodiment or thepropagating illumination embodiment.

To this point, the optics have been integral to the medium proper, or toa cartridge in which the medium proper is housed. In the case ofpropagating light, when the optics were integral only to the cartridge,they served the purpose of working with the external drive objective toincrease numerical aperture to near 1. Here, the optics are againintegral to the cartridge, but serve as stand-alone objectives having anumerical aperture of about 0.6, in order to eliminate the need for thedrive objective.

A better embodiment, however, is to use integral optics both at themedium proper and at the cartridge, so that the two sets of optics worktogether as a high numerical aperture objective. Whether theillumination is propagating or evanescent, the numerical aperture willbe greater than 1 and typically 1.3 or higher.

The optics integral to the media are preferably, as before,circumferential in form, while the optics in the cartridge are either anarray of close packed lenses, staggered so that their fields of viewoverlap and completely cover the medium radius, or an array oflenticules, skewed with respect to the tracks in the medium so as tocover the entire data area (see FIGS. 29A and 29B).

The detector can be a single detector that is actuated radially toreceive the signal from the various elements in the optical array, ormay be a small detector array that is similarly actuated. However, apreferred detector arrangement, in which radial actuation is eliminated,follows.

Skewed Detector Array

Whether the optical array is integral to the medium cartridge or is inthe drive, and whether this array is combined with additional integraloptics in the medium proper, the resulting image from each of the arrayelements contains information from many data tracks simultaneously. Adetector array may be placed along and oriented parallel to thelongitudinal axis of the optical element, in the focal plane of theoptical element, as seen in FIG. 37. Each of the individual detectorpixels 194 in the array then receive the signal from a given data track192 within the image from the optical element. Therefore, by monitoringthe signal from each of detector pixels 194 either switching between oneat a time or several at once, the data from multiple tracks can be readsimultaneously and at high speed.

For the higher track pitches reached with the evanescent fieldillumination, for example, the size of the detector pixel should be assmall as possible. At present, the CCD (including CMOS) industry makespixels as small as 6 microns square. However, substantially sub-pixelresolution can be synthesized by aligning the boundary between twodetector columns with the optical axis of the optical array element,such that each of the optical artifacts in the image plane of theoptical element is swept in a skewed trajectory across the detectorboundary. By analyzing the signal output from several contiguousdetector pixels in those two rows, and because the amount of skewbetween the detector columns, optical array element, and data track arepreset and known, optical artifacts that are significantly smaller thanthe detector pixel are detected and resolved from neighboring opticalartifacts.

Pixels in a CCD, CMOS, or other detector are usually arranged in anarchitecture of straight rows and columns. Resolution of such a detectoror display with this architecture is determined by, and on the order of,the size of the pixel in each axis relative to the image or other lightpattern presented to it or displayed. Should a part of the light patternoverlap several pixels, the centroid of the light pattern can bedetermined to a fraction of a pixel. However, should a light pattern besmaller than a pixel, it is not resolved whether it falls within a pixelor straddles plural pixels.

In the case of detection, the skewed pixel columns allow the kind ofsub-pixel centroid resolution described above, except that the sub-pixelsized object itself is resolved rather than its centroid alone.

Because the size of the offset from one pixel to another is known, therelative signal levels from each of the pixel "channels" can be comparedand analyzed to detect, resolve, and determine the size of the sub-pixellight pattern as it traverses the terminator boundary between theneighboring pixel columns. The optimum way of doing this depends onwhether speed or resolution or noise reduction is the over ridingconcern. The pixel to pixel analysis algorithm can be as simple as(A-B)/(A+B), in the typical quad-cell detector mode, or can be much moresophisticated as iterations involving a larger number of pixels isinvolved.

A mask 196 may be added that is an array of apertures centered on thepixel column boundaries. The width of the apertures is on the order ofthe resolution required. Such a mask 196 may also be centered on thepixel columns, but the benefit of the pixel detection arithmetic iseliminated.

This method and means is somewhat analogous to a Vernier scale, which isto say a Moire or heterodyning technique, where resolution on a scalemuch smaller than the fiducials on the Vernier or the grating pitch inMoire is achieved. However, it also shares elements of the centroidresolution of the quad-cell, and even some elements of a knife-edgeapproach.

This skewed array architecture can be applied to an entire 2-D detectorchip, or to a bi, tri, or multi-linear array. In optical data storage,reduces or eliminates the need for servo tracks (acts as wobble pitservo); reduces or eliminates radial movement and actuator in opticaldrive: a tri-linear array of about a 20 mm length would cover the entirearea of a spinning 50 mm (e.g., Polaroid Mini Disc), thereby making fora drive nearly the size of the medium with reduced mechanisms and cost,and allows parallel data readout, multi-channel encoding, and extremelyfast readout and data transfer rates. Where smaller storage capacity issufficient, a staggered architecture CCD or CMOS detector could eveneliminate spinning the medium as well, so that a rectangular data chipcould be read out directly (with or without near-field).

A further advantage can be gained by adding a small fixed slope to thedetector plane and/or to the optical array plane, relative to the planeof the medium, such that the center point of the slope is vertically atand intersects the plane of best focus. This eliminates the need for afocus servo because the slope is calculated such that the amount ofpossible defocus from vertical movement of the medium or other reasonsis encompassed by the total slope. In other words, the optical artifactwill always be in focus somewhere along the detector column length.

Whole-Field Imaging

Whole-field imaging can be used in many ways as exemplified by thesystem diagram of FIG. 38. New encoding schemes in which multiple tracksare used together would allow even more density in data storage. Withthe existing encoding, multitasking from the same disc is possible, asseveral software programs can be read from the same disc at the sametime. Rotation speed can be reduced because data transfer is occurringfrom several tracks at once, rather than having to wait for the disc toprogress a full rotation. Therefore, data transfer rates can be as highor higher than hard disk drives, for example. At present, removablemedia storage devices that are not based on the Winchesters hard disctechnology are much slower in data transfer times, so they cannotcompete for that part of the desktop PC market.

The whole-field imaging advantage brought by the integrated micro--opticarray is best realized with near-field illumination and optics. However,even propagating illumination techniques will enjoy a good increase ineffective NA up to but less than 1 for the media cartridge integration,and more for integration to the medium proper.

For some applications, data can be read from a non-rotating medium,whether that medium is circular in form or rectangular or other, bycombination and extension of this invention of integrating micro-opticswith the medium and the system combination with a secondary array ofoptics and a multi-element areal detector array. The data is scannedfrom the disc without mechanical movement of any kind, by reading outthe detector array signal. Writing would require a similar array oflaser diodes and at least a linear movement relative between the mediumand the laser diode array. When optical active layers become moresensitive, however, a whole-field approach can be applied to the writingaspect as well, where a whole-field illumination source is spatiallymodulated by an optical gating device such as a liquid crystal matrix,placed at the focus plane conjugate to the detector plane.

In the embodiment of the optical array with a non-actuated singleillumination source for reading and or writing, additional optics notshown are inserted between the source and the array in order to make thesystem optically telecentric. Otherwise, a multiple source array may beused.

Other applications:

In addition to optical data storage applications, the integration ofmicro-optic arrays with a surface or photo-active surface has otherapplications not anticipated prior to this. The micro-optic array can beflexible, semi-rigid, or rigid.

For example, in the mastering of the stamper for ROM discs, integrationof a film of micro-lenticulars with the photoresist would increase themastering resolution, allowing a wider choice of laser wavelengths andtherefore a wider variety of photoresists. The micro-lenticulars wouldbe removed along with the resist later in the process.

Resolution in micro-lithography of, for example, micro-electroniccircuits and devices would be improved by integration of a micro-opticarray with the photo-resist coated semiconductor wafer, thereby allowingsmaller line widths and more powerful, faster chips, without resortingto a single, costly, large immersion objective. In this application, themicro-optics could be aligned with the line pattern itself.

Similarly, a micro-optic array could be applied to a finished processedwafer in order to measure line widths with high resolution. Themicro-optic array would preferably consist of micro--aplanatic lensesused either in immersion mode or in near-field mode, and would allow thesame or better resolution as an oil immersion objective but without theimmersion oil, which could contaminate a clean room and ruin anexpensive micro-electronic wafer.

That same micro-optic array can be integrated to many surfaces andsamples other than wafers, so that even inexpensive microscopes with,for example, an objective with NA of 0.65 or so would be converted toimmersion microscopes with NAs of better than 1 and typically NAs ofabout 1.3, without oil and with the high working distance of the NA 0.65objective. While an immersion objective lens can cost several hundred toseveral thousands of dollars, the flexible micro-optic arrays would bemass-produced by, for example, compression molding or web-embossing, andso would be repeatable yet inexpensive and disposable.

Flexible immersion lenses:

The present invention removes the need for immersion oil in photontunneling microscopy as well as immersion microscopy, eliminates theexpensive immersion objective, and allows photon tunneling with a dry,long working distance, lower NA objective.

In the Guerra flexible transducer patents of 1994 and 1996, the rigidtotal internal reflection surface is eliminated and replaced with adisposable, inexpensive, precision transducer. However, an oil immersionobjective must still be oil-contacted to the transducer. This inventiontakes the flexible transducer a step further, and eliminates the oilimmersion objective by incorporating integral micro-aplanatic lenses,arranged in a close-packed array into the upper transducer surface. Withthis flexible optical sheet placed on the sample in the teaching of thetransducer patents, a dry long working distance objective of numericalaperture 0.6 will function together with the integral aplanatic lensesas an oil immersion objective of NA 1.25 or higher. In this way photontunneling, or even just immersion microscopy, is accomplished withoutoil and with a large working distance. Of course, what is lost is theability to move the aplanat with respect to the sample, but with theclose packed array most of the sample will be made visible by moving thedry objective relative to the micro-lenses.

This flexible lens array brings affordable photon tunneling andimmersion microscopy to the classroom, for example, or to applicationswhere the immersion oil is thought to be a problem, such as in thesemi-conductor industry when used for lithography or metrology. It iseasily molded or embossed into web, or the lenses can be holographicelements.

The present invention removes the need for immersion oil in photontunneling microscopy as well as immersion microscopy, eliminates theexpensive immersion objective, and allows photon tunneling with a dry,long working distance, lower NA objective.

In the Guerra flexible transducer patents of 1994 and 1996, the rigidtotal internal reflection surface is eliminated and replaced with adisposable, inexpensive, precision transducer. However, an oil immersionobjective must still be oil-contacted to the transducer. This inventiontakes the flexible transducer a step further, and eliminates the oilimmersion objective by incorporating integral micro-aplanatic lenses,arranged in a close-packed array into the upper transducer surface. Withthis flexible optical sheet placed on the sample in the teaching of thetransducer patents, a dry long working distance objective of numericalaperture 0.6 will function together with the integral aplanatic lensesas an oil immersion objective of NA 1.25 or higher. In this way photontunneling, or even just immersion microscopy, is accomplished withoutoil and with a large working distance. Of course, what is lost is theability to move the aplanat with respect to the sample, but with theclose packed array most of the sample will be made visible by moving thedry objective relative to the micro-lenses.

This flexible lens array brings affordable photon tunneling andimmersion microscopy to the classroom, for example, or to applicationswhere the immersion oil is thought to be a problem, such as in thesemi-conductor industry. It is easily molded or embossed into web, orthe lenses can be holographic elements. Polaroid is world-class in allof these technologies.

If in the future the pixel size in CCD arrays is made smaller to thepoint where optical resolution is exceeded, a micro-optic array integralto the CCD would increase the resolution accordingly. (Now just used forfill efficiency, back thinned too.)

Recording media can be for optical data recording or for imagerecording.

Harmonic generation

For most of the evanescent field applications discussed thus far, thewavelength, or quasi-wavelength, of the evanescent field is the same asthat of the parent wave in the denser medium, which in these cases arethe integral micro-optics or the integral resonance structure. Thefrequency of the evanescent field, however, is invariant with the indexof the medium. If, however, the total internal reflection occurs withina photo-refractive non-linear material, second harmonics can begenerated when the incidence of the light it close to the criticalangle, such that the frequency of the evanescent field is doubled. Inthis case, it becomes possible to consider other active optical layersin which the mechanism for change is molecular in nature, in the form ofphoto-dissociation of bonds. (This can be seen to have impact on a scopewider than optical data storage, if, for example, the integralnear-field optics are used with water as the active optical layer andthe illumination is sunlight made sufficiently coherent, such that thehydrogen to hydrogen bonds in the water are broken to release hydrogenfor fuel (with desalination a useful byproduct when ocean water isused).) Further discussion is provided in Bloembergen and Lee.

Vertical Storage: Multilayer, Multilevel

Integrating the near-field optics with the medium also, by definition,makes the near-field part of the medium. The stability that this impartscompared to a flying near-field head that is part of the drive ratherthan the medium, for example, facilitates the full use of the evanescentfield component. Thus, for example, diffraction-born evanescent fieldswith their very short decay become more practical to use, as alreadydiscussed. The stable evanescent field may also be better applied forvertical storage in two forms. The first is multilevel, where varyingthe intensity of the illumination causes a corresponding variable changein the optical bit in the active optical layer, such that rather than abinary-encoded data set one may encode in many levels. The high opticalcontrast (signal to noise) that results from evanescent fieldillumination of, for example, either magneto-optical or phase changeactive layers, allows many more levels to be achieved than with thenormal propagating light for reasons stated earlier.

A second form of vertical storage made possible with the integralevanescent field is called multi-layer (see FIG. 39), because the totalreflection interface at which the evanescent field arises can berepeated vertically with the addition of subsequent layers ofhigh-low-high refractive index materials, where the refractive index mayeven be complex if the absorber is thin enough. In this way, refocusingthe external objective lens or array causes information stored at eachof these total reflection interfaces to rapidly come into focus. Thenumber of vertical data layers is restricted by the scatteringproperties of the layers, particularly the active layers, in addition tothe accumulation of unfocussed light from the nearest active layers, sothat in practice the signal to noise ratio is too low if four or moreactive layers are used. In the example provided, three signals 202, 204,and 206 are returned from three such layer configurations.

See FIG. 40 for an example of signals returned from a storage mediumhaving a four-layer configuration. Trace 202t represents the signal fromthe first high-low interface, trace 204t represents the signal from thesecond high-low interface, trace 206t represents the signal from thethird high-low interface, and trace 208t represents the signal from thefourth and most distant high-low interface.

If the vertical periodicity of the high-low layer elements is on theorder of 20 microns or less, with the low index being less than a micronthick, there is an interesting but unexplained equal splitting of thesignal from each of the active layers, rather than the expectedprogressive splitting, or halving, of the signal from each of thepreceding active layers. For greater vertical periodicity, the signalsplits as expected such that the signal from the lowest is quite weak.In this case it is useful to make the vertical periodicity non-linear bymaking the furthest low index layers progressively thinner to compensatefor the weaker return signal. A greater vertical periodicity, althoughadding somewhat to the layer structure complexity, allows betterseparation of the signal from each of the active layers by the depth offocus of the external objective combined with the integrated near-fieldoptics.

Integral micro-optics can also be used when the method of opticalstorage is holographic in nature.

While the invention has been described with reference to particularembodiments, it will be understood that the present invention is by nomeans limited to the particular constructions and methods hereindisclosed and/or shown in the drawings, but also comprises anymodifications or equivalents within the scope of the claims.

What is claimed is:
 1. A storage medium, suitable for use with anexternal source of illumination for the storage and retrieval ofinformation, said storage medium comprising:an optical layer disposed toreceive the illumination, said optical layer comprising a plurality ofmicro-optical elements, each said micro-optical element having a firstindex of refraction and configured such that illumination incident uponsaid micro-optic element produces local evanescent field illuminationextending from said optical layer, and an active layer disposed toreceive said evanescent field illumination, said active layer beingresponsive to said evanescent field illumination such that apredetermined amount of said evanescent field illumination impingingupon a portion of said active layer produces an artifact within saidportion.
 2. The storage medium of claim 1 wherein said active layercomprises at least one of the following materials: crystalline phasechange material, amorphous phase change material, dye absorber,chalcogenide glass and compounds, polymer, quartz, magneto-opticalmaterial, photo-refractive polymer, photo-refractive crystal,photographic emulsion, fluorescent material, photoresist, binary medium,or semiconductor detector array.
 3. The storage medium of claim 1wherein said artifact comprises a change in at least one of thefollowing characteristics of said active layer: index of refraction,scatter, optical phase, polarization, diffraction, refraction,constructive interference, destructive interference, absorption,magneto-optical Kerr rotation, surface topography, chemical structure,mechanical structure (e.g., adhesion), or material phase state.
 4. Thestorage medium of claim 1 wherein said micro-optical element furthercomprises a prism-like optic.
 5. The storage medium of claim 4 whereinsaid prism-like optic comprises a truncated prism.
 6. The storage mediumof claim 1 wherein micro-optical element further comprises a lens havingcurvature in at least one meridian.
 7. The storage medium of claim 6wherein said curvature is aplanatic.
 8. The storage medium of claim 6wherein said curvature is aspherical.
 9. The storage medium of claim 1wherein said optical layer further comprises a resonant structure. 10.The storage medium of claim 9 wherein said resonant structure comprisesa layer of material having a second index of refraction.
 11. The storagemedium of claim 10 wherein said second index of refraction is less thansaid first index of refraction.
 12. The storage medium of claim 10wherein said second index of refraction is greater than or equal to saidfirst index of refraction.
 13. The storage medium of claim 10 whereinsaid material comprises a metal.
 14. The storage medium of claim 13wherein the thickness of said metal layer is selected such that asurface plasmon resonant field is generated in response to the incidentillumination.
 15. The storage medium of claim 1 wherein said opticallayer further comprises a diffraction grating.
 16. The storage medium ofclaim 15 wherein said diffraction grating has a spatial period smallerthan the illumination wavelength.
 17. The storage medium of claim 1further comprising a substrate disposed upon said active layer.
 18. Thestorage medium of claim 17 wherein said substrate comprises one of thefollowing materials: polycarbonate, mylar, glass, acrylic, andpolyester.
 19. The storage medium of claim 17 wherein said substratecomprises means for providing tracking guidance.
 20. The storage mediumof claim 1 further comprising a layer of material having a third indexof refraction disposed between said active layer and said optical layer,said third index of refraction being smaller than said first index ofrefraction.
 21. The storage medium of claim 20 wherein said materialcomprises air.
 22. The storage medium of claim 20 wherein said layer ofmaterial comprises a thickness of dimension less than the wavelength λof the source of illumination.
 23. The storage medium of claim 1 furthercomprising a housing.
 24. The storage medium of claim 23 wherein saidhousing comprises a window.
 25. The storage medium of claim 24 whereinsaid window comprises micro-optical elements.
 26. The storage medium ofclaim 1 wherein said optical layer further comprises means for providingtracking guidance.
 27. The storage medium of claim 26 wherein said meansfor providing tracking guidance comprises secondary optical artifacts.28. The storage medium of claim 1 wherein said micro-optical elementcomprises dihedral surfaces.
 29. The storage medium of claim 1 furthercomprising a second active layer disposed proximal to said active layer.30. The storage medium of claim 29 further comprising a separation layerhaving a third index of refraction, said separation layer disposedbetween said active layer and said second active layer.
 31. The storagemedium of claim 30 wherein said third index of refraction is less thansaid first index of refraction.
 32. The storage medium of claim 1wherein said active layer comprises means for providing trackingguidance.
 33. A storage medium, suitable for use with an external sourceof illumination, having a wavelength λ, for the storage and retrieval ofinformation, said storage medium comprising:an optical layer disposed toreceive the illumination, said optical layer comprising a plurality ofmicro-optical elements, each said micro-optical element having a firstindex of refraction and configured such that illumination incident uponsaid micro-optic element produces propagating illumination extendingfrom said optical layer, said optical layer further comprising aninterference reference surface, and an active layer disposed to receivesaid propagating illumination, said active layer being responsive tosaid propagating illumination such that a predetermined amount of saidpropagating illumination impinging upon a portion of said active layerproduces an artifact within said portion.
 34. The storage medium ofclaim 33 wherein said micro-optical element further comprises aprism-like optic.
 35. The storage medium of claim 34 wherein saidprism-like optic comprises a truncated prism.
 36. The storage medium ofclaim 33 further comprising a substrate disposed upon said active layer.37. The storage medium of claim 36 wherein said substrate comprises oneof the following materials: polycarbonate, mylar, glass, acrylic, andpolyester.
 38. The storage medium of claim 36 wherein said substratecomprises means for providing tracking guidance.
 39. The storage mediumof claim 33 wherein said optical layer further comprises means forproviding tracking guidance.
 40. The storage medium of claim 39 whereinsaid means for providing tracking guidance comprises secondary opticalartifacts.
 41. The storage medium of claim 33 further comprising asecond active layer disposed proximal to said active layer.
 42. Thestorage medium of claim 41 further comprising a separation layer havinga third index of refraction, said separation layer disposed between saidactive layer and said second active layer.
 43. The storage medium ofclaim 42 wherein said third index of refraction is less than said firstindex of refraction.
 44. The storage medium of claim 33 wherein saidmicro-optical element comprises dihedral surfaces.
 45. A storage medium,suitable for use with an external source of illumination for the storageand retrieval of information, said storage medium comprising:a firstoptical layer comprising micro-optical elements, said first opticallayer further comprising a first index of refraction and disposed toreceive the illumination and generate an evanescent field illuminationtherefrom; a second optical layer comprising a second index ofrefraction, said second optical layer disposed to receive saidevanescent field illumination and generate a secondary evanescent fieldillumination therefrom, and an active layer disposed to receive saidsecondary evanescent field illumination, said active layer beingresponsive to said secondary evanescent field illumination such that apredetermined amount of said secondary evanescent field illuminationimpinging upon a portion of said active layer produces an artifactwithin said portion.
 46. The storage medium of claim 45 wherein saidsecond optical layer comprises a total internal reflection surface. 47.The storage medium of claim 45 wherein said first index of refraction issubstantially equivalent to said second index of refraction.
 48. Thestorage medium of claim 45 wherein said second optical layer comprises aresonant structure.
 49. The storage medium of claim 48 wherein saidresonant structure comprises a layer of material comprising an index ofrefraction lower than said first optical layer index of refraction. 50.The storage medium of claim 49 wherein said material comprises air. 51.The storage medium of claim 45 wherein said first optical layer combineswith said second optical layer to form aplanatic optical elements. 52.The storage medium of claim 45 wherein said active layer comprises atleast one of the following materials: crystalline phase change material,amorphous phase change material, dye absorber, chalcogenide glass andcompounds, polymer, quartz, magneto-optical material, photo-refractivepolymer, photo-refractive crystal, photographic emulsion, fluorescentmaterial, photoresist, binary medium, or semiconductor detector array.53. The storage medium of claim 45 wherein said artifact comprises achange in at least one of the following characteristics of said activelayer: index of refraction, scatter, optical phase, polarization,diffraction, refraction, constructive interference, destructiveinterference, absorption, magneto-optical Kerr rotation, surfacetopography, chemical structure, mechanical structure (e.g., adhesion),or material phase state.
 54. The storage medium of claim 45 wherein saidmicro-optical element further comprises a prism-like optic.
 55. Thestorage medium of claim 54 wherein said prism-like optic comprises atruncated prism.
 56. The storage medium of claim 45 whereinmicro-optical element further comprises a lens having curvature in atleast one meridian.
 57. The storage medium of claim 56 wherein saidcurvature is aplanatic.
 58. The storage medium of claim 56 wherein saidcurvature is aspherical.
 59. The storage medium of claim 45 furthercomprising a metal disposed upon said second optical layer.
 60. Thestorage medium of claim 59 wherein the thickness of said metal layer isselected such that a surface plasmon resonant field is generated inresponse to the incident illumination.
 61. The storage medium of claim45 wherein said second optical layer further comprises a diffractiongrating.
 62. The storage medium of claim 61 wherein said diffractiongrating has a spatial period smaller than the illumination wavelength.63. The storage medium of claim 45 further comprising a substratedisposed upon said active layer.
 64. The storage medium of claim 63wherein said substrate comprises one of the following materials:polycarbonate, mylar, glass, acrylic, and polyester.
 65. The storagemedium of claim 45 further comprising a layer of material having a thirdindex of refraction disposed between said active layer and said opticallayer, said third index of refraction being smaller than said firstindex of refraction.
 66. The storage medium of claim 65 wherein saidlayer of material comprises a thickness of dimension less than thewavelength λ of the source of illumination.
 67. The storage medium ofclaim 45 further comprising a housing.
 68. The storage medium of claim67 wherein said housing comprises a window.
 69. The storage medium ofclaim 68 wherein said first optical layer is disposed upon said window.70. The storage medium of claim 45 wherein said second optical layerfurther comprises means for providing tracking guidance.
 71. The storagemedium of claim 70 wherein said means for providing tracking guidancecomprises secondary optical artifacts.
 72. The storage medium of claim45 wherein said active layer comprises means for providing trackingguidance.
 73. The storage medium of claim 63 wherein said substratecomprises means for providing tracking guidance.
 74. The storage mediumof claim 45 further comprising a second active layer disposed proximalto said active layer.
 75. The storage medium of claim 74 furthercomprising a separation layer having a third index of refraction, saidseparation layer disposed between said active layer and said secondactive layer.
 76. The storage medium of claim 75 wherein said thirdindex of refraction is less than said first index of refraction.
 77. Thestorage medium of claim 45 wherein said active layer comprises at leastone of the following materials: crystalline phase change material,amorphous phase change material, dye absorber, chalcogenide glass andcompounds, polymer, quartz, magneto-optical material, photo-refractivepolymer, photo-refractive crystal, photographic emulsion, fluorescentmaterial, photoresist, binary medium, or semiconductor detector array.78. The storage medium of claim 45 wherein said artifact comprises achange in at least one of the following characteristics of said activelayer: index of refraction, scatter, optical phase, polarization,diffraction, refraction, constructive interference, destructiveinterference, absorption, magneto-optical Kerr rotation, surfacetopography, chemical structure, mechanical structure (e.g., adhesion),or material phase state.
 79. A storage medium, suitable for use with anexternal proximal source of evanescent field illumination provided bymeans of an optical element having an index of refraction for thestorage and retrieval of information, said storage medium comprising:anoptical layer comprising an index of refraction, said optical layerdisposed to receive the evanescent field illumination and generatesecondary evanescent field illumination therefrom, and an active layerdisposed to receive said secondary evanescent field illumination, saidactive layer being responsive to said secondary evanescent fieldillumination such that a predetermined amount of said secondaryevanescent field illumination impinging upon a portion of said activelayer produces an artifact within said portion.
 80. The storage mediumof claim 79 wherein said optical layer comprises a total internalreflection surface.
 81. The storage medium of claim 79 wherein saidoptical layer index of refraction is substantially equivalent to theoptical element index of refraction.
 82. The storage medium of claim 79wherein said optical layer comprises a resonant structure.
 83. Thestorage medium of claim 82 wherein said resonant structure comprises alayer of material comprising an index of refraction lower than theoptical element index of refraction.
 84. The storage medium of claim 83wherein said material comprises air.
 85. The storage medium of claim 79wherein said optical layer combines with the optical element to form anaplanatic optical element.
 86. The storage medium of claim 79 furthercomprising a metal disposed upon said optical layer.
 87. The storagemedium of claim 86 wherein the thickness of said metal layer is selectedsuch that a surface plasmon resonant field is generated in response tothe incident illumination.
 88. The storage medium of claim 79 whereinsaid optical layer further comprises a diffraction grating.
 89. Thestorage medium of claim 88 wherein said diffraction grating has aspatial period smaller than the illumination wavelength.
 90. The storagemedium of claim 79 further comprising a substrate disposed upon saidactive layer.
 91. The storage medium of claim 90 wherein said substratecomprises one of the following materials: polycarbonate, mylar, glass,acrylic, and polyester.
 92. The storage medium of claim 90 wherein saidsubstrate comprises means for providing tracking guidance.
 93. Thestorage medium of claim 79 further comprising a housing.
 94. The storagemedium of claim 93 wherein said housing comprises a window.
 95. Thestorage medium of claim 79 wherein said optical layer further comprisesmeans for providing tracking guidance.
 96. The storage medium of claim95 wherein said means for providing tracking guidance comprisessecondary optical artifacts.
 97. The storage medium of claim 79 whereinsaid active layer comprises means for providing tracking guidance. 98.The storage medium of claim 79 further comprising a second active layerdisposed proximal to said active layer.
 99. The storage medium of claim98 further comprising a separation layer having a third index ofrefraction, said separation layer disposed between said active layer andsaid second active layer.
 100. The storage medium of claim 99 whereinsaid third index of refraction is less than said first index ofrefraction.